Abstract: Methods and systems are described for the estimation of recent shared ancestry (ERSA) from the number and lengths of identical-by-descent (IBD) nucleotide segments derived from, e.g., high-density single-nucleotide polymorphism data or whole-genome sequence data. ERSA is accurate to within one degree of relationship for 97% of first- through fifth-degree relatives and 80% of sixth- and seventh-degree relatives. ERSA's statistical power approaches the maximum theoretical limit imposed by the fact that distant relatives frequently share no DNA through a common ancestor. ERSA greatly expands the range of relationships that can be estimated from genetic data.