The superior angular resolution of the Hubble Space Telescope allows us to conduct high precision optical photometry of the the stellar populations of nearby dwarf irregular galaxies. This photometry allows us to re-construct their recent star formation histories. By concentrating on the core helium burning phase of stellar evolution, (as opposed to the core hydrogren burning phase - the "main sequence") it is possible to reconstruct unambiguous, detailed star formation histories over the last 1 billion years. A comparison of four galaxies observed to date indicates that these galaxies experience relatively long periods (~1 billion years) of both elevated and depressed star formation - producing a picture of episodic star formation (as opposed to either relatively constant or "bursting" star formation).

Abundance analysis of the interstellar medium provides an independent check on these star formation histories. By comparing the abundances of elements produced in massive stars (e.g., oxygen) with those of elements produced in intermediate mass stars (e.g., nitrogen) it is possible to estimate the time elapsed since the last episode of star formation. This nucleosynthesis test has been shown to be in agreement with the recently available star formation histories (e.g., Skillman et al. 1997 ApJ, 474, 205).

Dwarf galaxies are the primary targets for helium abundance measurements required for determining the primordial helium abundance (Yp), a constraint on the standard model of Big Bang Nucleosynthesis (e.g, Skillman et al. 1994, ApJ, 431, 172). Presently, systematic uncertainties represent the greatest source of uncertainty in Yp (e.g., Olive et al. 1997, ApJ, 483, 788.) The systematic uncertainty of the chemical evolution histories of these galaxies will be discussed within the context of other uncertainties.