Ecologists and institutionalists challenge the :lSSLllllption underlying • conti1Jgency and transaction cost analysts that organizations can readily change tlieir basic structural fcalur~s, Ibther, Lhey suggesl that organizations are relatively inertial structures, difficult to change. Change is viewed as hard, rare, and, indeed, dangerous to the I'iability of organizations. Rather than being planned or internally induced, the sources of change are often located in the wider environment-in the dynamics of population-level demographic processes or in political demands and normative pressures stemming from, for t'xample, the nation-state or tl~e professions. To understand these processes, we need to ask questions such as: How are organizations, and new types of organizations created? vVhy dOl they increase or decrease in numbers? vVhy do they faiP How do wider political, social ane! cultural factors shape the structlire and fate of organizations? How do collections of diverse organizations engaged in related activities interact, seek stability, and undergo significant change? Ve begin by rel'iewing sJme of the insights associated wilh ecological theory and then iritroduce thel arguments of institutional scholars. These two approp complemenlary formUlations.] in,st'veral