This chapter gives an overview of the bioequivalence criteria as applied in the European union. The main focus is on immediate release formulations, including study design, Test and Reference products, subjects, study conduct, characteristics to be investigated (i.e., AUC and Cmax, parent drug or metabolite, chiral drug substances, use of urinary data, and endogenous substances), strength to be investigated, and estimation of bioequivalence. Furthermore, estimation of bioequivalence of highly variable drug or drug products, narrow therapeutic index drugs and orodispersible tablets are addressed. For more complex formulations, such as locally applied drug products and modified release oral and transdermal dosage forms, additional criteria are needed to show bioequivalence, as stipulated in this chapter. In vivo data are not required in all cases to conclude bioequivalence and in vitro data may be sufficient. This includes a waiver for oral solutions and application of the Biopharmaceutics Classification System based biowaiver, with reference to the ICH M09 guideline. Further guidance is provided by product specific guidances and Question and Answers documents to address specific issues in bioequivalence.