Komatiite-hosted sulfide deposits are an important source of base and precious metals globally. This Ph.D. thesis comprises a synopsis and four original papers dealing with komatiite-hosted Archean and Paleoproterozoic Ni-Cu-PGE sulfide deposits in Finland, focusing on their geological, mineralogical, and lithogeochemical characterization, PGE content, and petrogenesis. In Finland, no significant komatiite-hosted Ni-Cu-PGE deposits have so far been discovered, although several small, low-grade deposits occur in Archean and Paleoproterozoic greenstone belts in eastern and northern Finland. Some of the studied deposits, which are associated with low-Mg komatiite to komatiitic basalt magmatism, are substantially enriched in PGE. The occurrence of komatiitic rocks with a clear signal of assimilation of external sulfur, their similarity with ore-bearing komatiitic rocks worldwide, and the discovered mineralization demonstrate that Finnish komatiitic rocks, and the mafic-ultramafic magmatism in general, have considerable exploration potential for Ni-Cu-PGE ores, as shown by the recently discovered Sakatti Cu-Ni-PGE deposit in Central Lapland. This thesis deepens our understanding of the Finnish deposits, and the results can be utilized in mineral exploration.