Large-scale and high-throughput approaches play an essential role in the study of the highly complex biological systems. In plant biology, obtaining the complete genome sequence of the model plant Arabidopsis thaliana has definitively encouraged the incorporation of a completely new set of tools for the identification, characterization, and quantification of its proteome. Proteomics is a new branch of the protein sciences that makes use of these tools and the set of experimental methods specifically designed for them. In this chapter, we describe a complete method for the isolation, fractionation, and identification of a set of proteins obtained from Arabidopsis thaliana cells, stressing methodological aspects that could be of potential interest.