Compared with cellulose, the primary component of the paper we use every day, nanocellulose has a much smaller diameter (typically <10 nm) that renders it many unique properties. Amongst many others, these properties include high mechanical strength, large surface area and low visual light scattering. Nanocellulose can be obtained by disintegration of plant cellulose pulp or by the action of specific types of bacteria. Once produced, nanocellulose can be used to make transparent films, fibers, hydrogels, or aerogels that exhibit extraordinary mechanical, thermal, and optical properties. Each of these substrates is a suitable template or carrier for inorganic nanoparticles (NPs), thus enabling production of nanocomposites that possess properties of the two constituents. In this review, we focus on the preparation of nanocellulose, nanocellulose films, and nanocellulose papers, and introduce nanocellulose-based nanocomposites and their environmental applications.