In this chapter we present the main achievements in the development of catalysts based on microporous and mesoporous molecular sieves for the production of light olefins and BTX aromatics as the main basic building blocks for the manufacture of petrochemicals. The first part of the chapter covers the relevant aspects of processes aimed at producing light olefins from crude oil via catalytic cracking of gasoil and naphtha fractions, oxidative dehydrogenation (ODH) of short-chain alkanes, and from oil-alternative carbon sources such as natural gas or biomass as offered in methanol-to-olefins (MTO) processes. In the second part, we discuss the salient features of zeolites in the production of BTX aromatics via aromatization of LPG, naphtha reforming, and methane dehydroaromatization (MDA). Finally, given the industrial relevance of para-xylene as petrochemical intermediate, processes for its production from less valuable aromatics, including isomerization of xylenes and ethylbenzene, disproportionation/transalkylation of toluene, and alkylation of toluene with methanol, using zeolites with enhanced shape-selective properties are also reviewed. As highlighted in this chapter, catalysts relying on micro- and mesoporous molecular sieves are pivotal to improving the efficiency of already commercialized processes, and to the successful implementation of new technologies that are currently at different stages of development.