**1. Introduction**

As renewable and biodegradable nanomaterials, nanocelluloses have raised a huge interest for several decades. Indeed, their natural available and abundant source—the biomass—as well their interesting properties makes them materials of choice for new nanomaterial science in a large panel of applications. Two types of nanocelluloses exist: cellulose nanofibrils (CNF) and cellulose nanocrystals (CNC) differing from each other in their properties as well in their isolation process. As presented in **Figure 1**, the exponential evolution of the number of publications and patents dealing with cellulose nanocrystals confirms the large interest generated by these nanomaterials.

This chapter aims to describe CNC isolation from cellulose using classical or more recent methods, as well as their properties and applications.

**Figure 1.**

*Noncumulative evolution of the number of publications and patents dealing with CNC (source: SciFinder, April 2019—Descriptors, cellulose nanocrystal, cellulose nanorod, rodlike cellulose, cellulose nanowire, cellulose crystallite, cellulose nanoparticle, cellulose whiskers, nanocrystalline cellulose—Language, English).*
