Ring-opening metathesis polymerization (ROMP) of cyclic olefins enables the synthesis of useful materials that are all but impossible to prepare by other means. For example, a variety of commercial polymers, such as Vestenamer®, Norsorex®, Telene®, Metton®, Zeonex®, and Zeonor® 2 are produced on large scale with ROMP, while more specialized materials are being investigated for applications ranging from drug delivery to photolithography. The chemistry that underwrites these polymerizations is the olefin metathesis reaction in which metal alkylidenes react with olefins, thereby shuffling their alkylidene fragments to generate new olefin products. Among the most important catalytic systems for olefin metathesis are those based on W, 5 Ti, Mo, and Ru. While the value of ROMP has been apparent for many decades, there has been a strong desire to find ROMP catalysts that are based on more earth-abundant, less expensive, and less toxic elements. In this regard, intriguing recent developments in the use of iron catalysts have been reported, although the applicability of these systems is still an open question. On the other hand, there are some polymer applications for which the presence of metal contaminants is unacceptable, such as in the areas of drug delivery, biomedical implants, or microelectronics, which thus necessitates often difficult purification procedures. For this reason and others, it would be of great interest to use abundant main-group elements to achieve olefin ROMP. Unfortunately, designing functionality that effectively mimics the reactivity of metal alkylidenes is not trivial. Creative work by Boydston using photocatalysis for certain ROMP reactions notwithstanding, the development of a broadly applicable olefin ROMP strategy that uses simple, organic catalysts remains an open challenge.