This work is motivated by questions and polemics related to religion and belief in God's existence, and also decision about what to believe and on what basis. It is illustrated the main thesis of pragmatism, a philosophical tradition that originated in the second half of the nineteeth century according to which all the beliefs and theories we posses should serve and be of use in practice and in our daily action and should ensure success and reliability in the field of personal, but also social interests. The first part of this work is is devoted to the pragmatic understanding of the truth by William James, a philosopher that is given credit for its development after he elaborated the idea of Charles Peirce. Peirce asserted that our beliefs are in fact rules for action and James defines true theories as being the best instruments for action because they serve as means to achieve all life satisfaction. The truth, for pragmatists, has the function to lead as to what is the most useful and worthwhile. Conforming to that, pragmatism is turning from rationalism and from searching the objective truth and accepts the plurality of truth. The central part of the work focuses on the issue of rationality of religious beliefs in view of the lack of conclusive and experiential evidence for the existence of God. Even so, it is possible to offer pragmatic arguments in support of theism and their basis is to show and point to the benefit of religious beliefs for practical life. Pascal's Wager and James's Will to Believe are the two most famous theistic pragmatic arguments and they are exposed in this work. In conclusion, there is a connection to fideism, the view that faith is not dependent on proof and personal opinion that the nature of true faith is not necessary linked to rationality and absolute objectivity, but rather to one’s inner feelings and hope.