The growing demand for plant-based protein concentrates and isolates has led to the search for sustainable alternatives to energy- and water-intensive wet fractionation processes. Dry fractionation, which involves dry milling followed by air classification, is a sustainable and energy-efficient way to enrich plant proteins from various agro-materials, such as legumes, oilseed meals, cereals, and brans. Dry milling is a crucial step because it must optimally break down the protein-starch cell matrix to separate the protein bodies from the larger starch granules. Air classification separates the fine protein-rich particles from the coarse carbohydrate-rich particles based on their size and density differences. Centrifugal air classifiers are the most common type of classifier used for this purpose in agro-materials. This chapter outlines a clear procedure for milling and air classification of red lentils to produce protein-rich fine fractions. The classifying mill was optimized to obtain red lentil flour with a particle size (D90) of 40–42 μm to achieve maximum separation of protein bodies from the cell matrix. The flour is passed through an air classifier with pre-optimized settings to obtain a protein-rich fine fraction with a particle size (D90) of 20–22 μm. Detailed explanations of the milling and air classification steps are provided in this chapter to help other researchers operate and develop dry fractionation processes for other materials.