This document summarizes the taxonomy, natural habitats, modes of infection, identification techniques, and antimicrobial susceptibility of various aerobic and anaerobic actinomycetes. It describes how Nocardia, Rhodococcus, Streptomyces, and Actinomadura are soil-dwelling aerobic actinomycetes that can cause opportunistic infections in humans. It also discusses how Actinomyces species are normal inhabitants of human mucous membranes and can cause actinomycosis. Identification and diagnosis of these genera involves examining colony morphology, acid-fast staining, and biochemical profiling.