This review consists of the following three sections: (1) General principles in selecting antimycobacterial drugs for the treatment regimens, (2) The antimicrobial activity in vitro with an emphasis on inhibitory and bactericidal potency of various agents, and (3) Drug susceptibility testing including methodology and interpretation of the test results. Each of these sections addresses three groups of antimycobacterial agents: (1) against tuberculosis, (2) against Mycobacterium avium complex infections, and (3) against infections caused by M. fortuitum and M chelonae. The following are the drugs examined in the sections and subsections of this review: isoniazid, ethionamide, thiacetazone, rifampin, rifabutin, rifapentine, KRM-1648, pyrazinamide, streptomycin, kanamycin, amikacin, capreomycin, gentamicin, tobramycin, ethambutol, para-aminosalicylic acid, D-cycloserine, ofloxacin, levofloxacin, ciprofloxacin, sparfloin, clofazimine, clarithromycin, azithromycin, erythromycin, cefoxitin, cefmetazole, imipenem, sulfamethoxazole, sulfisoxazole, sulfadiazine, sulfathiazole, trimethoprim, and doxycycline.