Polymer composites are materials in which the matrix polymer is reinforced with organic or inorganic fillers or reinforcements of a definite size and shape, resulting in the enhanced performance of the resultant composite. Both thermosetting and thermoplastic polymers can be used as the matrix material. Biocomposites, on the other hand, are made of biodegradable polymers and natural fibres. Polymer composites and biocomposites can be classified as hybrid composites when different types of fibres are used in a single matrix, and nanocomposites when nanomaterials are used as reinforcement in the composites. These composite materials find a wide range of applications in such diverse fields as 3D printing, geotextiles, construction, electronics, medical, packaging, and automobiles.