Human chlamydial infections remain a substantial microbiological and public-health challenge because members of the genus Chlamydia depend on intracellular growth, produce diverse clinical syndromes and frequently escape clinical recognition. Chlamydia trachomatis causes common sexually transmitted infections, trachoma and neonatal disease, whereas C. pneumoniae and C. psittaci are associated with respiratory and zoonotic disease. This structured narrative review synthesizes recent advances in taxonomic characterization, developmental biology, molecular host–pathogen interactions, immune-mediated stress responses, clinical diagnosis, treatment and genomic surveillance. Particular emphasis is placed on the biphasic elementary-body/reticulate-body cycle, the inclusion membrane and type III secretion effectors, and the role of interferon-gamma–associated nutrient restriction in experimentally observed persistence. Nucleic acid amplification tests provide the foundation of contemporary diagnosis, although assay accuracy varies by platform and specimen and nucleic acid detection does not establish bacterial viability. Current treatment recommendations prioritize doxycycline for uncomplicated C. trachomatis infection in nonpregnant adults, with specific exceptions for pregnancy and invasive or zoonotic syndromes. The literature supports a clear distinction between laboratory persistence, reinfection, residual post-treatment nucleic acid and genetically mediated resistance. We highlight the potential of validated point-of-care tests, direct-from-sample genomics and viability-oriented approaches, while identifying translational uncertainties and surveillance gaps. A structured search approach is documented without claiming systematic review methodology.