Textiles release fibres to the environment during production, use, and at end-of-life disposal. Approximately two-thirds of all textile items are now synthetic, dominated by petroleum-based organic polymers such as polyester, polyamide and acrylic. Plastic microfibres (<5 mm) and nanofibres (<100 nm) have been identified in ecosystems in all regions of the globe and have been estimated to comprise up to 35% of primary microplastics in marine environments, a major proportion of microplastics on coastal shorelines and to persist for decades in soils treated with sludge from waste water treatment plants. In this paper we present a critical review of factors affecting the release from fabrics of microfibres, and of the risks for impacts on ecological systems and potentially on human health. This review is used as a basis for exploring the potential to include a metric for microplastic pollution in tools that have been developed to quantify the environmental performance of apparel and home textiles. We conclude that the simple metric of mass or number of microfibres released combined with data on their persistence in the environment, could provide a useful interim mid-point indicator in sustainability assessment tools to support monitoring and mitigation strategies for microplastic pollution. Identified priority research areas include: (1) Standardised analytical methods for textile microfibres and nanofibres; (2) Ecotoxicological studies using environmentally realistic concentrations; (3) Studies tracking the fate of microplastics in complex food webs; and (4) Refined indicators for microfibre impacts in apparel and home textile sustainability assessment tools. (C) 2018 The Authors. Published by Elsevier B.V.