Significant efforts have been made to fabricate drug-loaded nano particles for drug delivery. Nanoprecipitation is a simple and versatile method for making various types of polymer nanoparticles with well-controlled particle size, size distribution, and surface properties. This review presents a critical overview of three different widely used nanoprecipitation techniques, namely, traditional nanoprecipitation in bulk solutions, flash nanoprecipitation, and microfluidic-based nanoprecipitation. The review starts with the comparison of these three different nanoprecipitation methods summarizing their key characteristics, advantages, and disadvantages. Then, different types of nanoparticles synthesized using nanoprecipitation are presented including di-block copolymer nanoparticles and natural polymer nanoparticles. A special focus is placed on comparing different drug-loaded polymer nanoparticles prepared using different nanoprecipitation approaches including their synthesis methods, drug loading, encapsulation efficiency, nanoparticle properties (e.g., size, PDI, etc.), and stability. Finally, the principle of forming nanoparticles with well-controlled properties is discussed to fundamentally understand the intricate interplay between mixing, supersaturation, nucleation, and particle growth, aiming to provide a general guideline for making drug-loaded nanoparticles based on nanoprecipitation.