Abstract. An elliptic BC n generalization of the classical two parameter Bailey Lemma is proved, and a basic one parameter BC n Bailey Lemma is obtained as a limiting case. Several summation and transformation formulas associated with the root system BC n are proved as applications, including a 6 ϕ 5 summation formula, a generalized Watson transformation and an unspecialized Rogers-Selberg identity. The last identity is specialized to give an infinite family of multilateral Rogers-Selberg identities. Standard determinant evaluations are then used to compute B n and D n generalizations of the Rogers-Ramanujan identities in terms of determinants of theta functions. Starting with the BC n 6 ϕ 5 summation formula, a similar program is followed to prove an infinite family of D n Euler Pentagonal Number Theorems.