Ecological stoichiometry is a field of study that connects the elemental compositions of living organisms to interactions occurring at various levels within ecosystems, ranging from cellular metabolisms to abiotic-biotic interactions. We will begin by examining the elemental compositions that make up an organism and the importance of maintaining the mass balance within an individual organism. We will investigate the relationship between metabolic rates and the stoichiometry of organisms, as well as explore different strategies employed to maintain stoichiometric homeostasis. Moving beyond the individual level, we will delve into how stoichiometric requirements influence resource competition within a community. Additionally, we will examine how variations in stoichiometry between prey and predator impact the dynamics and efficiency of trophic transfers within food webs. Finally, at the ecosystem level, we will explore the intricate nutrient cycling processes that are regulated by the stoichiometry of both the community and the abiotic environment.