  In this work we perform the symmetry classification of the Klein Gordon
equation in Bianchi I spacetime. We apply a geometric method which relates the
Lie symmetries of the Klein Gordon equation with the conformal algebra of the
underlying geometry. Furthermore, we prove that the Lie symmetries which follow
from the conformal algebra are also and Noether symmetries for the Klein Gordon
equation. We use these resutls in order to determine all the potentials in
which the Klein Gordon admits Lie and Noether symmetries. Due to the large
number of cases and for easy reference the results are presented in the form of
tables. For some of the potentials we use the Lie admitted symmetries to
determine the corresponding invariant solution of the Klein Gordon equation.
Finally, we show that the results also solve the problem of classification of
Lie/Noether point symmetries of the wave equation in Bianchi I spacetime and
can be used for the determination of invariant solutions of the wave equation.
