  We present the results of Halpha imaging of 94 irregular galaxies, including
types Im, BCD, and Sm. The sample spans a large range in galactic parameters
including integrated absolute magnitude (MV=-9 to -19), average surface
brightness (20 to 27 mag/arcsec2), current star formation activity (0 to 1.3
Msun/yr/kpc2), and relative gas content (0.02 to 5 Msun/LB). The Halpha images
were used to measure integrated star formation rates and extents of star
formation and to compare azimuthally-averaged radial profiles of current star
formation to older starlight. The integrated star formation rates of Im
galaxies normalized to the physical size of the galaxy span a range of a factor
of 10^4 with 10% Im galaxies and one Sm system having no measurable star
formation at the present time. The BCDs fall at the high end of the range of
rates. We find no correlation between star formation activity and proximity to
other catalogued galaxies. The cases with strong gradients in the L(Halpha)/LV
ratios and with high central star formation rate densities, which include most
of the BCDs, require a significant fraction of their gas to have migrated to
the center in the last Gyr. We discuss possible torques that could have caused
this without leaving an obvious signature, including dark matter bars and past
interactions or mergers with small galaxies or HI clouds. There is now
substantial evidence for these processes among many surveys of BCDs. The star
formation process itself does not appear to differ much among BCD, Im and Sm
types. There is evidence in the distribution function for Halpha surface
brightness, which is always approximately log-normal, that the turbulent Mach
numbers are about the same in these systems.
