The discovery that Streptococcus pneumoniae uses a competence-stimulating peptide (CSP) to induce competence for natural transformation， and that other species of the mitis and the anginosus streptococcal groups use a similar system， has expanded the tools to explore gene function and regulatory pathways in streptococci. Two other classes of pheromones have been discovered since then， comprising the bacteriocin-inducing peptide class found in Streptococcus mutans (also named CSP， although different from the former) and the SigX-inducing peptides (XIP)， in the mutans， salivarius， bovis， and pyogenes groups of streptococci. The three classes of peptide pheromones can be ordered from peptide synthesis services at affordable prices， and used in transformation assays to obtain competent cultures consistently at levels usually higher than those achieved during spontaneous competence. In this chapter， we present protocols for natural transformation of oral streptococci that are based on the use of synthetic pheromones， with examples of conditions optimized for transformation of S. mutans and Streptococcus mitis.