Bees, both commercially managed honey bees and wild bees, play an important role in global food production. In the United States, the value of honey bees only as commercial pollinators in U.S. food production is estimated at about $15 billion to $20 billion annually. Given their importance to food production, many have expressed concern about whether a "pollinator crisis" has been occurring in recent decades. World-wide reports indicate that populations of both managed honey bees and native bees have been declining, with colony losses in some cases described as severe or unusual. Aside from the range of potential identified causes for bee colony declines, this book addresses what role, if any, pesticides play in influencing the health and wellness of bees. The book begins by describing what is known about managed and wild bee populations, continues with brief descriptions of factors that might be affecting those populations, including a more detailed look at the potential effects of pesticide exposures and risk management.