The development of olefin metathesis has revolutionized the fields of organic and polymer chemistry. However, its dependence on rare and expensive transition metal catalysts raises concerns regarding long-term sustainability and limits its use in applications that necessitate being free from metal contaminants. This dissertation describes the development of metal-free olefin metathesis reactions enabled by hydrazine and diazene catalysis. Chapter 1 provides a historical and mechanistic overview of olefin and carbonyl-olefin metathesis. The origins of catalytic olefin metathesis are traced from its first observations at DuPont in the 1950s, to the widespread adoption of highly reactive metal-carbene catalysts in modern organic chemistry. The focus then shifts to carbonyl-olefin metathesis, charting its evolution from photochemically mediated reactions to modern catalytic platforms, with special attention given to hydrazine-catalyzed methods. Chapter 2 details a highly efficient, metal-free ring-opening metathesis polymerization of cyclobutenes using a hydrazine catalyst. This polymerization proceeds with living characteristics, giving precise control over molecular weight and low dispersities. Additionally, a variety of functional groups are tolerated, highlighting the method’s synthetic versatility. Chapter 3 describes the development of an oxidative alkyl-halide olefin metathesis reaction. Utilizing benzo[c]cinnolines as catalysts, a variety of coumarin and quinolone derivatives are synthesized. The ability to apply this method to other electrophiles is also demonstrated in the first example of oxidative alcohol-olefin metathesis. This method serves as a blueprint for the development of future metal-free metathesis reactions.