  Perfect fluid with kinematic self-similarity is studied in 2+1 dimensional
spacetimes with circular symmetry, and various exact solutions to the Einstein
field equations are given. In particular, these include all the solutions of
dust and stiff perfect fluid with self-similarity of the first kind, and all
the solutions of perfect fluid with a linear equation of state and
self-similarity of the zeroth or second kind. It is found that some of these
solutions represent gravitational collapse, and the final state of the collapse
can be either black holes or naked singularities.
