Electrical conductivity of single-walled carbon nanotube (SWNT)-epoxy composites (see Figure) is investigated as a function of SWNT concentration, mean length, and aggregation. The composites exhibit a percolation-like conductivity with threshold volume fractions as low as 5.2 x 10(-5). These low thresholds are attributed to continuous nanotube chains that form in the semi-dilute concentration regime; higher thresholds result when aggregation is inhibited.