Poly (lactic acid) or polylactide (PLA) is a well-developed commercial biobased, biodegradable, biocompatible, and non-toxic polymer that has competitive material and processing costs and high mechanical properties. Thereby, it can highly be considered for biomedical applications and as the most promising substitute for a wide range of commodity and engineering applications where non-compostable petroleum-based polymers are being used. PLA also possesses series of serious shortcomings such as low melt strength, slow crystallization kinetics, poor processability, formability, and foamability, high brittleness, low toughness, and low service temperature which limit its production and usage. To overcome these limitations, blending PLA with other polymers has been known as an inexpensive breakthrough which could also tailor the final properties of the PLA-based products. During the last two decades, researchers have investigated the synthesis, processing, characterization, and development of various PLA-based blend systems including miscible blends of poly L-lactide (PLLA) and poly D-lactide (PDLA), which generate stereocomplex crystals, binary immiscible/miscible blends of PLA with other thermoplastics, multifunctional ternary blends using a third blending polymer or fillers such as nanoparticles, as well as PLA-based blend foam systems. This study reviews these investigations and compares the syntheses/processing-morphology-properties interrelationships in PLA-based blends developed thus far for various applications.