Analytical validation strategies are developed based on the biomarker characteristics, technology platform, intended use, and clinical application of the companion diagnostic. Validation considerations differ for quantitative, semi-quantitative, and qualitative assays. Our approach considers assay-specific performance characteristics, sample type and availability, biomarker prevalence, biomarker-positive and biomarker-negative representation, sample size requirements, and the appropriateness of surrogate or contrived specimens. Early validation planning helps ensure that analytical evidence is available when needed to support IDE applications, IVDR Article 58 and Annex XIV performance study submissions, trial enrollment, and biomarker-based patient selection. Validation plans, study protocols, and acceptance criteria are developed using applicable regulatory guidance, recognized consensus standards, and jurisdiction-specific requirements to support analytical and clinical performance validation.