This talk will focus on dwarf galaxies, the most numerous galaxy type in the Universe. These low mass galaxies are fundamental in understanding galaxy evolution, and galaxy formation models must be able to predict and describe their properties. However, recent observations suggest mutiple origins for the dwarf galaxy populations of nearby groups and clusters, suggesting they are not a simple, homogeneous population. In this talk, I will review our current understanding of dwarf galaxy formation and evolution. Using deep observations of nearby galaxy clusters, I will also show that the line between low mass galaxies and massive star clusters is becoming increasingly blurred, with increasing evidence that some ultra compact dwarfs are the stripped remnants of dwarf ellipticals rather than being massive globular clusters.