The formation of the largest gravitationally bound structures in the Universe, clusters of galaxies, and how these environments affect the galaxies within them are major themes in cosmology and galaxy evolution. The high-redshift progenitors of clusters, called "protoclusters", are still in the process of hierarchical assembly. The transition from protocluster to cluster is gradual, driven by accretion and spectacular mergers that are expected to last roughly one billion years. This workshop aimed to address open questions in protocluster and cluster formation, to define the similarities and distinctions between the two, and to evaluate the best tools and methods for their detection and study.