This book focuses on the synthesis, characterization, and applications of a variety of nanosized catalysts for the conversion of renewable energy (biomass/solar) into fuels and chemicals, clean hydrogen production, photoelectrochemical energy conversion processes, etc. Chapter 1 elucidates various factors intervening in oxide and oxide-composite supports of nanocatalysts in energy conversion. Chapters 2 and 3 summarize the role of nanocatalysis for renewable aromatics from biomass and biodiesel production, respectively. Chapter 4 discusses the role of hybrid electrocatalysts for oxygen electrode reactions. The applications of porous graphitic carbon nitride nanostructures and 2D transition metal carbides (MXenes) for photocatalytic hydrogen evolution reaction and electrocatalysis are summarized in Chapters 5 and 6, respectively. Chapter 7 provides the advances and challenges in Pt-free Pd-based catalysts for oxygen electro-reduction in alkaline media. Chapter 8 reports the applications of the morphology-and size-selective Pd-based electrocatalysts for fuel cell reactions. The significance of Prussian blue analogues and nanostructured graphene oxide-based catalysts for H2O2 production and Fischer-Tropsch synthesis are highlighted in Chapters 9 and 10, respectively. Chapter 11 addresses the production of light olefin via catalytic oxidative cracking. The magic of heterogeneous nanocatalysis in VLPC for sustainable organic synthesis is discussed in Chapter 12. Hydrogen generation from ammonia borane using various metal nanoparticle-based catalysts is summarized in Chapter 13. The book covers various aspects of nanocatalysis and nanosized catalysts, including synthesis, characterization, and their role in achieving energy sustainability. Thus, the book will be of great interest to researchers/students and industrial chemists familiar with the fields of heterogeneous catalysis and nanocatalysis. We hope that catalysis researchers will find this book as a key reference for the fundamental understanding of surface science, rational catalyst design, and the applications of various nanocatalysts for energy applications. We would like to thank the authors for accepting the invitation and submitting the chapters to this book. We also thank the production team at Wiley for their invaluable assistance and support. © 2023 John Wiley & Sons Ltd. All rights reserved.