We introduce the bisector energy of an n-point set P in R 2 , defined as E(P) = (a, b, c, d) ∈ P 4 | a, b have the same perpendicular bisector as c, d .If no line or circle contains M (n) points of P, then we prove that for any ε > 0We also derive the lower bound E(P) = Ω(M (n)n 2 ), which matches our upper bound when M (n) is large. We use our upper bound on E(P) to obtain two rather different results:(i) If P determines O(n/ √ log n) distinct distances, then for any 0 < α ≤ 1/4, either there exists a line or circle that contains n α points of P, or there exist Ω(n 8/5−12α/5−ε ) distinct lines that contain Ω( √ log n) points of P. This result provides new information on a conjecture of Erdős [7] regarding the structure of point sets with few distinct distances.(ii) If no line or circle contains M (n) points of P, the number of distinct perpendicular bisectors determined by P is Ω min M (n) −2/5 n 8/5−ε , M (n) −1 n 2 . This appears to be the first higher-dimensional example in a framework for studying the expansion properties of polynomials and rational functions over R, initiated by Elekes and Rónyai [2].