In the paper we present a branch and price approach to routing and spectrum allocation – a basic optimization problem in elastic optical networks. We formulate the problem as a mixed-integer program for which we develop a branch and price algorithm enhanced with such techniques as cutting planes for improving lower bounds for the optimal objective value, and a greedy and a simulated annealing heuristics for improving the upper bounds. All these elements are combined into an effective optimization procedure. Preliminary results show that the algorithm is able to produce optimal solutions and in a vast majority of the considered cases it performs better than a standard branch-and-bound method implemented in the CPLEX solver.