The dynamics of social movements after their initial emergence is stil
l largely terra in-cognita. I develop a theory of the dynamics of prot
est waves by comparing data on protests in West Germany between 1965 a
nd 1989 with similar data from the Netherlands, Italy, and the United
States. Striking similarities are noted among these different protest
waves in the development of action repertoires, levels of repression a
nd facilitation, and the involvement of different types of organizatio
ns. An explanation for these dynamic patterns combines external and in
ternal factors: The interplay between facilitation, repression, and th
e chance of success defines a set of external constraints that combine
with activists' choices among three strategic options - innovation, i
ncreased participation, or increased militancy.