Editor's Note: To measure activity in the middle market, Mergers & Acquisitions looks at transactions that fulfill several requirements: Deals must have a value of roughly $1 billion or less; they must be completed (not just announced) within the timeframe designated; and they must include at least one U.S. company in the role of buyer and/or seller. Excluded from our charts are: recapitalizations; self-tenders; exchange offers; repurchases; stake purchases; and transactions with undisclosed values, buyers or sellers. Our data provider is Thomson Reuters, which updates its databases continuously. We use the data available at press time. For this article, data was collected on Dec. 31, 2014.

Browse charts and graphs:

2014 Best Year for Middle-Market M&A Since 2007

Month-by-Month Look at 5 Years of Mid-Market M&A

Sensata's Acquiring of Madison Dearborn-Backed Schrader Tops List of Mid-Market Deals in 2014

Top Mid-Market Deals by Industry

Most Active Mid-Market Investment Banks

Most Active Mid-Market Law Firms