Advanced Therapy Medicinal Products (ATMPs) represent a revolutionary frontier in medicine, offering life-changing treatments for conditions previously deemed incurable. However, the intricate nature of these therapies, from their unique raw materials to complex manufacturing and logistics, presents significant challenges and inherent risks. This Guide offers practical guidance on applying validation methods and control throughout the cell and gene therapy product lifecycle. It outlines risk-based strategies tailored to the unique nature of these products, addressing key areas such as analytical methods, equipment, processes, cleaning, and supply chain. It also includes essential insights into regulatory expectations and phase-appropriate considerations that support timely development and commercialization. Developed for professionals in cell and gene therapy, this ISPE Guide: ATMPs – Validation Methods and Controls Throughout the Cell and Gene Therapy Product Lifecycle provides actionable insights to help navigate the complex ATMP landscape. It promotes flexible, science-driven development approaches that support informed decision-making and help accelerate patient access to these transformative therapies.