Biodegradable polymers are emerging polymeric materials with application in the biomedical, pharmaceutical and packaging fields. Blending is a simple and effective route to develop new materials with tailored properties, and this review reports the advances in the field of biodegradable polymer blends with both natural and synthetic polymers. First, the theoretical background necessary to understand the miscibility behaviors observed in real polymer blends are provided. The simple but highly flexible Flory‐Huggins theory is examined, incorporating the regular solution theory to account for the enthalpic contribution. This simple theoretical model is extended with the appropriate approaches to systems presenting specific interactions, providing a quite detailed overall picture of the miscibility behavior of polymer blends. The second section reviews the structure, preparation, miscibility and properties of different biodegradable polymer blends investigated up to now. Particularly, the biodegradable blends based on polylactides (PLAs), poly(ϵ‐caprolactone) (PCL), poly(3‐hydroxybutyrate) (PHB), poly(p‐dioxanone) (PPDO) and polyglycolide (PGA) have been reviewed.