The World Health Organisation (WHO) bioequivalence (BE) guidance has remained stable between the publication of the first edition of this book and the present update. Although the WHO guideline has been republished in the years between editions of this chapter, the content related to bioequivalence has remained mostly unchanged. However, the pending adoption of the ICH Harmonised Guideline M13A Bioequivalence for Immediate Release Sold Oral Dosage Forms will trigger a review of the WHO guideline under the oversight of the WHO Expert Committee for Specifications for Pharmaceutical Preparations. The WHO does not adopt ICH guidelines directly because of differences in the development and consultation procedures for guideline development between the two entities but, it is expected that a new WHO guidance will be developed employing the ICH M13A guideline as a framework. The WHO biowaiver (BW) guidance, on the other hand, has evolved in the time between previous editions of this chapter. The adoption of the ICH Harmonised Guideline M9 Biopharmaceutics Classification System-based Biowaivers, which was implemented by the WHO Prequalification Team—Medicines but, as mentioned above, cannot be adopted as a WHO guidance, triggered an assessment of the WHO BW guidance. This has ultimately led to the introduction of a new WHO BW guideline in 2024 and this revision is discussed in this updated chapter.