ABSTRACTMicroorganisms inhabit all possible biosphere ecosystems, including natural and man‐made subterranean environments, which favour the growth of specialized microbial communities under near‐starvation conditions. Among the most enigmatic microbial features found in karstic and volcanic caves are reticulated filaments, consisting of long mineralized filaments forming an open‐mesh with square‐shaped or hexagonal‐shaped reticles. Despite their widespread occurrence and detailed morphological documentation, their microbial origins, formation mechanisms and ecological roles remain enigmatic. This review consolidates current knowledge on reticulated filaments, and addresses theoretical and scientific gaps on these intricate microbial structures, highlighting the association of reticulated filaments with biomineralization processes and the potential involvement of rare or uncultivated microbial taxa. Variations in sheath composition and size suggest the involvement of multiple microbial groups, potentially including bacteria, archaea and fungi. This study proposes that reticulated filaments serve as biosignatures, reflecting complex microbe–mineral interactions and local geochemical conditions. Their occurrence in environments rich in iron and manganese points to potential biogeochemical cycling roles, while their structural complexity suggests adaptive strategies for microbial survival. Future research directions are outlined and the relevance of reticulated filaments as indicators of past and present microbial activity is highlighted, with implications for understanding biomineralization, geomicrobiology and the search for life in extreme environments.