Candida albicans is the most prevalent cause of vulvovaginal candidiasis ('yeast infection') and recurrent vulvovaginal candidiasis, though the incidence of non-albicans yeast species is increasing. The azole fluconazole is the primary antifungal drug used to treat R/VVC yet isolates from some species have intrinsic resistance to fluconazole, and recurrent infection can occur even with fluconazole-susceptible populations. The second-line broad-spectrum antimicrobial drug, boric acid, is an alternative treatment that has been found to successfully treat complicated VVC infections. Far less is known about how boric acid inhibits growth of yeast isolates in different morphologies compared to fluconazole and about the propensity of C. albicans to develop BA resistance or tolerance (the ability of a subpopulation to grow slowly in high levels of drug). We found significant differences in drug resistance and drug tolerance between C. albicans, C. glabrata, and C. parapsilosis isolates, with the specific relationships dependent on both drug and phenotype. Population-level variation for both susceptibility and tolerance was broader for fluconazole than boric acid in all species. Unlike fluconazole, which neither prevented hyphal formation nor disrupted mature biofilms, boric acid inhibited C. albicans hyphal formation and reduced mature biofilm biomass and metabolic activity in all isolates in a dose-dependent manner. Variation in planktonic response did not generally predict biofilm phenotypes. We also evolved 12 replicates from eight different C. albicans isolates to BA to examine whether resistance and/or tolerance to BA would evolve. Surprisingly, evolved isolates became less resistant yet more tolerant to BA. Overall, this thesis demonstrates that boric acid is effective at inhibiting planktonic and biofilm Candida cells, and that boric acid tolerance is evolvable. These results give us important baseline information about how boric acid works, that we can use in future studies on females with vulvovaginal candidiasis.