Prostatitis encompasses a heterogeneous group of disorders classified by the NIH into four categories. Category I (acute bacterial prostatitis) involves ascending urethral infection or hematogenous seeding, most commonly by E. coli, Klebsiella, or Pseudomonas, causing intense neutrophilic infiltration of prostatic acini and stroma with glandular destruction, microabscess formation, and systemic inflammatory response. Category II (chronic bacterial prostatitis) features persistent bacterial colonization within prostatic calculi and ductal biofilms that resist antibiotic penetration due to the blood-prostate barrier and alkaline prostatic fluid that ion-traps many antibiotics. Category III (chronic prostatitis/chronic pelvic pain syndrome) is subdivided into IIIA (inflammatory, with WBCs in expressed prostatic secretions) and IIIB (non-inflammatory), and involves neurogenic inflammation, pelvic floor myofascial dysfunction, and central sensitization of pain pathways. Category IV is asymptomatic inflammatory prostatitis found incidentally. The prostatic acinar epithelium secretes PSA, citric acid, and zinc; inflammation disrupts this secretory function and elevates serum PSA, complicating prostate cancer screening interpretation.