Plant-based proteins are increasingly recognized for their environmental, ethical, and nutritional benefits. However, their digestibility varies due to factors such as molecular structure, amino acid composition, and processing methods. This review comprehensively analyzes methods used to assess plant protein digestibility, including in vivo, in vitro, and ex vivo approaches. While in vivo studies, particularly those using pigs, are considered the gold standard, in vitro and ex vivo models offer cost-effective and reproducible alternatives for simulating digestion. Additionally, antinutritional factors present in plant proteins can hinder digestibility, necessitating processing strategies such as fermentation, enzymatic hydrolysis, and high-pressure treatments to enhance protein bioavailability. Advances in evaluation techniques, including the Digestible Indispensable Amino Acid Score (DIAAS) and dynamic digestion models, offer more precise assessments of protein quality. By systematically comparing these methods, this review aims to guide food scientists and manufacturers in selecting appropriate evaluation strategies to improve the nutritional quality of plant-based protein products. Understanding the mechanisms influencing plant protein digestibility is essential for optimizing food formulations and supporting the broader adoption of sustainable protein sources in human diets.