Arthroplasty surgery, especially total hip arthroplasty (THA), is considered amongst the most successful surgical procedures of all time. However, complications may occur that are disabling for patients. Of all complications, periprosthetic joint infection (PJI) is one of the worst, requiring additional surgery and prolonged periods of antibiotic treatment, in a best-case scenario. In the last decades, an increasing number of studies on PJI have been performed, but we still have not won the battle against microorganisms: up to 2% of patient develop PJI after arthroplasty surgery. This thesis aims to further the cause of this fight against PJI. Treatment of PJI consists of both administration of antibiotic agents, and surgery; the treatment of choice depends on several different factors. We performed a survey study to show that diagnosis and treatment differed between hospitals and between the Netherlands and Belgium. The alpha-defensin test is subject of the next three chapters, which shows good sensitivity and specificity for all three currently used definitions. A laboratory study was perfomed, in which the novel endolysin XZ.700 showed good results in the static model and performed excellently in the dynamic model, and demonstrated no toxicity on human osteocyte-like cells. A report on the results of using topical gentamicin sponges in DAIR (debridement, antibiotics, irrigation and implant retention) treatment for PJI after THA showed a success rate of 70%, and duration of symptoms for more than four weeks was associated with treatment failure. The success of DAIR treatment was studied in a larger, multicenter cohort, in which a 66% success rate was found, and several factors were identified that contributed to treatment failure: a history of rheumatoid arthritis, late infection (more than two years after initial surgery), erythrocyte sedimentation rate (ESR) of more than 60 mm/hour at presentation, duration of symptoms of more than one week, and coagulase-negative Staphylococcus PJI. Fungal PJI is very uncommon, and a systematic review showed that fungal PJI should be treated, like chronic bacterial PJI, with two-stage revision. The last two chapters describe outcomes after one-stage and two-stage revision, which seem to be comparable to outcomes after hip revision surgery in general. The thesis is concluded with discussing the different chapters, and pointing out the important items in PJI diagnosis, treatment and outcome.