Genstar Capital, Audax, HarbourVest, Stone Point and Abry ranked as the top five most active U.S.-based private equity firms of 2018, based on the volume of completed deals, according to PitchBook. Here are Mergers & Acquisitions' profiles of the 21 firms that led the league tables in a robust year for dealmaking and fundraising. Related: Top investment banks in PE-backed deals: KPMG, Houlihan, GS, William Blair.

1. Genstar Capital (79 completed deals)

1. Genstar Capital (79 completed deals)

Genstar Capital, led by president and managing director Ryan Clark, is a San Francisco-based PE firm that has been investing in middle-market companies since 1988. Genstar partners with its management teams and a network of strategic advisors, including current and former C-level executives from the industries in which it invests. Genstar recently raised its largest fund ever at $7 billion. Earlier in 2019, Genstar-backed Drillinginfo has bought Cortex, a software provider for the energy sector. Genstar recently acquired Ohio Transmission Corporation (OTC), an industrial automation equipment distributor and technical service provider. The firm employs more than 40 professionals and manages funds with total capital commitments of about $17 billion. Genstar invests in targeted segments of only four sectors: financial services, software, industrial technology and healthcare, and focuses on global companies headquartered in North America. It is currently managing its eighth fund and is seeking investment opportunities in founder-owned companies, public company orphans, corporate carve-outs and traditional buyouts. Related: 10 PE firms share strategies for tech M&A.

2. Audax Group (62)

Audax Group, founded in 1999, invests in middle-market companies through Audax Private Equity and Audax Private Debt, currently managing more than $16 billion of assets overall. Audax Private Equity, based in Boston and San Francisco, takes a buy-and-build investment approach, partnering with established companies to create larger entities through acquisitions and organic growth. The firm has invested more than $5 billion in 120 platform investments and 750 add-on acquisitions. In 2019, Audax Private Debt, which is based in New York, has raised the Audax Direct Lending Solutions Fund with $1.65 billion of capital. The private equity team has more than 100 investments, transaction and operations professionals. Audax Private Equity’s investments are headquartered in the U.S. and Canada, with operations in 21 countries. The companies are in business and consumer services, healthcare, software and technology, chemicals, energy, engineered products and materials industries. Audax recently invested in Astute Inc., a provider of artificial intelligence-driven customer engagement, digital self-service, and consumer data management software, for undisclosed terms. Astute's customers include B&G Foods Inc. (NYSE: BGS), The Cheesecake Factory Inc. (NASDAQ: CAKE) and Delta Air Lines Inc. (NYSE: DAL).

3. HarbourVest Partners (54)

HarbourVest Partners is global private markets investment firm with more than $58 billion in assets under management as of yearend 2018, including primary fund investments, secondary investments and direct co-investments. The firm, founded in 1982, has invested more than $9 billion directly in operating companies, including companies in the communications, consumer, financial, healthcare, industrial and information technology sectors. It invests in buyout, growth equity and mezzanine stages. HarbourVest, has more than 500 professionals, including more than 100 investment professionals. Its offices are in Beijing, Bogotá, Boston, Hong Kong, London, Seoul, Tel Aviv, Tokyo and Toronto.

4. Stone Point Capital (45)

Stone Point Capital, a PE firm based in Greenwich, Connecticut, has raised more than $19 billion to invest in more than 100 companies since launching its first fund in 1994. Stone Point invests in 12 verticals within the financial services industry: asset and wealth management; advisory, broker dealers and merchant trading; banking institutions; managed care and healthcare services; human resources benefits and employer services; insurance distribution and services; insurance run-off; life insurance underwriting; outsourcing and technology; property and casualty insurance; real estate finance and services; and specialty finance/non-bank lenders. The firm targets $50 million to $500 million equity investments, taking both minority and majority positions, with a horizon of five to more than 10 years.

5. Abry Partners (41)

Abry Partners, a PE firm headquartered in Boston, focuses on investments in media, communications, insurance, business and information services, with industry expertise in broadband, business services, communications, cybersecurity, healthcare information technology, information services, insurance services, Internet of Things, logistics, media and Software-as-a-Service. Since its founding in 1989, Abry has completed more than $82 billion of transactions. The firm has $12 billion under active management in four fund strategies, targeting investments of $20 million to $200 million. Its flagship private equity fund is the $2.1 billion Abry Partners IX, with a $525 million Abry Heritage Partners fund focused on lower middle-market companies, a $1.05 billion structured equity investment fund and a $1.5 billion senior debt securities fund.

5. Kohlberg Kravis Roberts (41)

KKR & Co. (NYSE: KKR) is a global firm that manages private equity, energy, infrastructure, real estate and credit investments, plus it has partners that manage hedge funds and it provides financing and investments through a capital markets business. KKR was founded in 1976, and through 2018 the firm had completed PE transactions with about $595 billion of total enterprise value in about 20 industries. KKR’s PE business invests in management buyouts and build-ups, minority positions, public company toe-hold investments and growth capital opportunities. Its Americas PE teams focus on industrials, financial services, retail and consumer, energy, technology, media and communications, healthcare, and hospitality and leisure industries. KKR has offices in 20 cities across 15 countries.

7. CI Capital Partners (35)

CI Capital Partners, a New York-based middle market PE firm, focuses on investing in business services; distribution, transportation and logistics; healthcare services; and residential services sectors. The firm seeks to form partnerships with experienced management teams and entrepreneurs to build through add-on acquisitions, organic growth and operational improvements. Since its inception in 1993, CI Capital has acquired more than 320 companies worth about $10 billion in enterprise value, including 33 platform companies and more than 285 add-on acquisitions. The firm’s target equity investment range is $10 million to $150 million. Portfolio companies acquired by CI Capital since 2008 have produced four times the revenue they produced before acquisition, on average, according to the firm.

8. The Blackstone Group (34)

The Blackstone Group (NYSE: BX) is an investment firm with nearly 2,500 professionals in 23 offices around the world. Blackstone’s private equity business has $130 billion in assets under management and a portfolio of more than 95 companies with $82 billion in combined annual revenue. Blackstone recently raised its largest buyout fund. The firm, founded in 1985, has more than 250 PE professionals worldwide, with PE offices in New York, London, Dusseldorf, Mumbai, Singapore, Hong Kong and Sydney. Through its corporate PE group, Blackstone invests in growth equity opportunities; new and later-stage development projects in energy and power and related sectors; buy-and-build opportunities with smaller companies in large, fragmented industries; and leveraged buyouts of large and mid-cap global companies.

8. Canada Pension Plan Investment Board (34)

Canada Pension Plan Investment Board, or CPPIB, is an investment manager governed by the Canada Pension Plan that invests pension’s funds in private equity, public equities, real estate, infrastructure and fixed income instruments. CPPIB is headquartered in Toronto, with offices in Hong Kong, London, Luxembourg, Mumbai, New York, São Paulo and Sydney. As of Dec. 30, 2018, the pension’s fund totaled C$368.5 billion ($275 billion). The CPPIB group that makes direct investments in private companies in North America and Europe has more than 55 professionals. The group considers investments ranging from passive, minority positions to 100 percent control positions in all sectors excluding real assets, with a minimum investment size of C$100 million ($75 million).

10. Providence Equity Partners (32)

Providence Equity Partners is a global private equity firm focused on the media, communications, education and information industries with about $40 billion in aggregate capital commitments. The firm is headquartered in Providence, Rhode Island, with offices in New York and London. Since the firm’s inception in 1989, it has invested in more than 180 companies. Providence’s flagship PE team invests in companies ranging from growth capital opportunities and family-owned businesses to large buyouts and take-privates, mostly in North America and Western Europe. The firm established its Providence Strategic Growth Capital Partners affiliate in 2014 to focus on growth equity investments in lower middle-market software and technology-enabled service companies, primarily in North America.

11. Ares Capital (31)

Ares Capital Corp. (Nasdaq: ARCC) is a specialty finance company that makes debt and equity investments in private middle-market companies and power generation projects in the U.S. The company invests primarily in first- and second-lien loans and mezzanine debt, and to a lesser extent it makes equity investments. Ares is regulated as a business development company, and with $12.9 billion of total assets as of yearend 2018 it is the largest BDC as measured by total assets and market capitalization, according to Ares. Its portfolio is valued at about $12.4 billion, consisting of 344 portfolio companies backed by 167 private equity sponsors. Ares Capital is externally managed by a subsidiary of Ares Management Corp. (NYSE: ARES).

11. TA Associates Management (31)

11. TA Associates Management (31)

TA Associates, led by chairman and managing partner Brian Conway, is a global growth private equity firm with offices in Boston; Menlo Park, California; London; Mumbai; and Hong Kong, and about 85 investment professionals. The firm invests in technology, healthcare, financial services, consumer and business services industries, typically investing $70 million to $500 million in businesses valued at $100 million to $3 billion. In April, TA made a minority investment in Indira IVF, an India-based infertility treatment provider. In 2018, the firm invested about $2.8 billion in 17 new investments and 11 add-on investments, and it realized $3.4 billion in liquidity for completing seven company exits, eight partial sales, three equity recapitalizations and two public offerings. Since its 1968 start, the firm has raised $24 billion and invested in more than 500 companies. TA won Mergers & Acquisitions’ 2018 M&A Mid-Market Award for Private Equity Firm of the Year.

11. Aquiline Capital Partners (31)

Aquiline Capital Partners, based New York and London, is a private equity firm that invests in the financial services sector, including insurance, financial technology and services, investment management, and banking and credit companies. Since its start in 2005, the firm has invested more than $2.5 billion in 40 middle-market businesses in North America and Europe, including investments in start-ups, growth equity and buyout opportunities, corporate carve-outs, consolidations and turnarounds. Through its Aquiline Technology Growth Fund, the firm invests in early- and growth-stage technology companies serving the insurance and financial services industries, including insurance technology, asset management technology, benefits and retirement, security, data and analytics, and enterprise software.

11. The Riverside Co. (31)

11. The Riverside Co. (31)

The Riverside Co., led by co-CEOs Béla Szigethy and Stewart Kohl, is a global private equity firm with more than $8 billion in assets under management and more than 200 professionals worldwide. Riverside, based in Cleveland and New York, has made more than 600 investments since it was founded in 1988, with more than 90 companies in its private equity and structured capital portfolios. The firm focuses on investing in businesses valued at up to $400 million. Its private equity business includes teams focused on control buyouts of North American-based platform companies with $10 million to $35 million in last-12-months EBITDA and with less than $10 million in LTM EBITA; investments in growth-stage technology companies; and control buyouts of European, Australian and New Zealand-based companies. Riverside won Mergers & Acquisitions’ 2018 M&A Mid-Market Award for Private Equity Seller of the Year.

15. Warburg Pincus (30)

Warburg Pincus is a global private equity firm focused on growth investing with more than $43 billion in assets under management. Since its founding in 1966, Warburg Pincus has raised 17 private equity funds that have invested more than $73 billion in more than 855 companies in more than 40 countries. Its active portfolio includes more than 180 companies. The firm is headquartered in New York, with offices also in Amsterdam, Beijing, Hong Kong, Houston, London, Luxembourg, Mumbai, Mauritius, San Francisco, São Paulo, Shanghai and Singapore. Its investment teams are organized by sector, focusing on energy; financial services; healthcare and consumer; industrial and business services; and technology, media and telecommunications sectors.

16. The Carlyle Group (29)

The Carlyle Group (Nasdaq: CG) is a global investment firm with $216 billion under management. The firm’s corporate PE business, with 275 investment professionals in 22 offices, is invested in 180 portfolio companies through 33 buyout and growth capital funds. The buyout teams invest through funds with $75 billion under management that focus on the U.S. and other geographic areas globally, as well as technology and financial services. The growth teams invest through funds with $6 billion under management focused on middle-market and growth companies in the U.S., Asia and Europe. Since 1990, the corporate PE unit has invested $98 billion in equity in 626 transactions and generated nearly $82 billion in gains, according to the firm.

17. Thoma Bravo (28)

Thoma Bravo is a PE firm with offices in Chicago and San Francisco that manages private equity and credit funds with more than $30 billion of investor equity commitments. The firm focuses on software and technology, acquiring more than 200 companies valued at more than $50 billion in those industries over a 20-year span. It takes a buy-and-build investment approach, investing in growth initiatives and strategic acquisitions to drive long-term value. Thomas Bravo’s current private equity software portfolio includes 35 companies that generate more than $10 billion in revenue annually and employ more than 33,500 people. The firm recently closed Thoma Bravo Fund XIII at $12.6 billion in investor capital commitments.

17. Apax Partners (28)

Apax Partners is a London-based private equity firm that has raised funds with about $50 billion in total commitments over a more-than-40-year span. Apax funds invest in companies globally in technology and telecommunications, services, healthcare and consumer sectors. The firm reviews investment opportunities through investment teams focused on the four sectors, plus a team of executives with operating experience, plus executives from those teams who also have online or digital knowledge, and a financing team. The firm started out as a venture capital firm in the 1980s and shifted its focus to buyouts in the 1990s. In addition to its London headquarters, the firm has offices in New York, Hong Kong, Mumbai, Munich, Shanghai and Tel Aviv.

17. TPG Capital (28)

TPG Capital is a global alternative asset firm with more than $103 billion under management with investment and operational teams in Austin and Fort Worth, Texas; Beijing; Boston; Dallas; Hong Kong; Houston; London; Luxembourg; Melbourne; Moscow; Mumbai; New York; San Francisco; Seoul; and Singapore. TPG, founded in 1992, manages investments in private equity, growth venture, hedge funds, real estate, credit and public equity asset classes. The firm’s TPG Capital PE business has invested more than $50 billion through about 175 transactions since 1993. Its TPG Capital Asia manages more than $9.4 billion in PE assets. TPG Growth specializes in growth equity and middle-market buyout investments, with $13.2 billion under management.

17. H.I.G. Capital (28)

H.I.G. Capital is a global private equity that focuses on investing in small and medium-sized companies. The firm has more than $30 billion of equity capital under management and more than 350 investment professionals, with offices in Atlanta, Bogotá, Boston, Chicago, Dallas, Hamburg, London, Los Angeles, Luxembourg, Madrid, Miami, Milan, New York, Paris, Rio de Janeiro, San Francisco and São Paulo. H.I.G. invests in management-led buyouts or recapitalizations of established, profitable, manufacturing and service businesses, and in growth and development opportunities in high-growth companies. Since H.I.G. was founded in 1993, the firm has acquired more than 300 businesses the U.S., Europe and Latin America.

17. Insight Venture Partners (28)

Insight Venture Partners is a New York-based global venture capital and private equity firm with more than $20 billion under management. The firm invests in high-growth technology and software companies. Since Insight was founded in 1995, it has invested in more than 300 companies, completed more than 200 M&A transactions for its portfolio companies and fostered more than 40 initial public offerings. The firm advises its portfolio companies through its Insight Onsite program, providing advice targeted at product and technology, marketing, sales, strategy and M&A, talent, business development and customer success functions.