  In this work, the quantization of the most general Bianchi Type I geometry, with and without a cosmological constant, is considered. In the spirit of identifying and subsequently removing as many gauge degrees of freedom as possible, a reduction of the initial 6--dimensional configuration space is presented. This reduction is achieved by imposing as additional conditions on the wave function, the quantum version of the --linear in momenta-- classical integrals of motion (conditional symmetries). The vector fields inferred from these integrals induce, through their integral curves, motions in the configuration space which can be identified to the action of the automorphism group of Type I, i.e. $GL(3,\Re)$. Thus, a wave function depending on one degree of freedom, namely the determinant of the scale factor matrix, is found. A measure for constructing the Hilbert space is proposed. This measure respects the above mentioned symmetries, and is also invariant under the classical property of covariance under arbitrary scalings of the Hamiltonian (quadratic constraint). 
Conditional Symmetries and the Quantization of Bianchi Type I Vacuum   Cosmologies with and without Cosmological Constant