The use of natural fibre-reinforced polymer composite (NFPMC) is increasing day by day in industries and fundamental research because they are renewable, cheap, completely or partially recyclable and biodegradable. Plants, such as flax, cotton, hemp, jute, sisal, kenaf, pineapple, ramie, bamboo, banana, bagasse etc., as well as wood are used as a source of lignocelluloses fibres and applied as reinforcement in composites. NFPMC consists of reinforced natural fibre in polymer matrix and posses wide engineering applications due to their low cost, ease of fabrication, adequate mechanical properties and dimensional stability. NFPMCs can replace plastic parts in number of applications, viz. wash basins, bathtubs, sinks, shower cabins, washing racks, roof, halmet, pipes, tubes, automotive components etc. Extensive research has been undertaken with regard to fabrication and characterization of PMC containing natural fibres like jute, hemp, pineapple, bamboo and kenaf. The present book is focused on characterization of injection moulded sisal fibre reinforced recycled/virgin high density polyethylene composite with varying sisal content.