Selenoprotein N (SelN) deficiency causes several inherited neuromuscular disorders collectively termed SEPN1-related myopathies, characterized by early onset, generalized muscle atrophy, and muscle weakness affecting especially axial muscles and leading to spine rigidity, severe scoliosis, and respiratory insufficiency. SelN is ubiquitously expressed and is located in the membrane of the endoplasmic reticulum; however, its function remains elusive. The predominant expression of SelN in human fetal tissues and the embryonic muscle phenotype reported in mutant zebrafish suggest that it is involved in myogenesis. In mice, SelN is also mostly expressed during embryogenesis and especially in the myotome, but no defect was detected in muscle development and growth in the Sepn1 knock-out mouse model. By contrast, we recently demonstrated that SelN is essential for muscle regeneration and satellite cell maintenance in mice and humans, hence opening new avenues regarding the pathomechanism(s) leading to SEPN1-related myopathies. At the cellular level, recent data suggested that SelN participates in oxidative and calcium homeostasis, with a potential role in the regulation of the ryanodine receptor activity. Despite the recent and exciting progress regarding the physiological function(s) of SelN in muscle tissue, the pathogenesis leading to SEPN1-related myopathies remains largely unknown, with several unsolved questions, and no treatment available. In this review, we introduce SelN, its properties and expression pattern in zebrafish, mice, and humans, and we discuss its potential roles in muscle tissue and the ensuing clues for the development of therapeutic options.