Dwarf Irregular Galaxies of the Local Group: A Conference in honour of David Block and Bruce Elmegreen

Local Group dwarf irregulars (dIrrs) cover an enormous range in star formation properties. Here I discuss these tiny galaxies as probes of star formation at the extremes of low gas densities and low metallicities. We have learned that (1) Star formation is inefficient in dIrrs and yet at very low Σ_HI <0.5 M_{\odot}^{-2}) the star formation rate is higher than expected from a linear extrapolation from star formation at higher Σ_HI. (2) Star formation correlates with existing stars and stellar feedback could be important. (3) Stellar disks go on for a long ways, often with very regular surface brightness profiles and reaching very low Σ_HI. (4) Breaks in surface brightness profiles occur at about the same magnitude in both spirals and dwarfs, so something fundamental is taking place there. (5) Dwarf disks appear to grow from the "outside-in", contrary to spirals. (6) At low metallicity, star formation takes place in giant molecular clouds, but the photodissociation region is large.