We first devise a branching algorithm that computes a minimum independent dominating set with running time O∗(1.3351n)=O∗(20.417n)O∗(1.3351n)=O∗(20.417n) and polynomial space. This improves upon the best state of the art algorithms for this problem. We then study approximation of the problem by moderately exponential time algorithms and show that it can be approximated within ratio 1+ϵ1+ϵ, for any ϵ>0ϵ>0, in a time smaller than the one of exact computation and exponentially decreasing with ϵϵ. We also propose approximation algorithms with better running times for ratios greater than 3 in general graphs and give improved moderately exponential time approximation results in triangle-free and bipartite graphs. These latter results are based upon a new bound on the number of maximal independent sets of a given size in these graphs, which is a result interesting per se.