For human agent cooperation, reasoning about the partner is necessary to enable an efficient interaction. To provide helpful information, it is important not only to account for environmental uncertainties or dangers but also to maintain a sophisticated understanding of each other's mental state, a theory of mind. Sharing every piece of information is not a good idea, as some may be irrelevant at time or already known, leading to distraction and annoyance. Instead, an agent will have to estimate the novelty and relevance of information for the receiver, to trade off the cost of communication against potential benefits. We propose the concept of theory of mind based communication as principled formulation to ground an agents cooperative communication on an understanding of the receiver's mental states to support her awareness and action selection. Therefore we formulate the problem of whether, when and what information to share as a sequential decision process with the human belief as central source of uncertainty. The agent's communication decision is obtained online during interaction by combining a second level Bayesian inference of human belief with planning under uncertainty, evaluating the influence of communication on the human belief and her future decisions. We discuss the resulting behavior on an illustrative communication scenario with different uncertain state aspects that an observing agent can communicate to the actor.