Rapid advances in the field of plant biology, especially in plant cell biology, have created the need for methods that allow the localization of proteins in situ at subcellular resolution. Although in many cases recombinant proteins with fluorescent proteins can fulfill this task, antibody-based immunological detection of proteins is a complementary technique, which avoids the risk of inducing side effects by a fusion protein, such as misexpression, mistargeting, altered stability, or toxicity. Moreover, recombinant protein techniques are applicable only to a rather limited set of model plants. The immunolocalization protocols presented here can be used to display protein localization patterns in different tissues of various plant species. This chapter describes a whole mount immunolocalization protocol, which has been extensively used in Arabidopsis roots and some above-ground tissues, and that also works in other species. Additionally, for bulky or hard tissue types, a variation of this protocol for paraffin-embedded sections is given.