This paper examines how the rules of the IMF and their implementation affect the voting power of its member countries and its capacity to make decisions, and makes recommendations for changes. Fundamental decision making at the IMF uses a system of weighted voting in which member countries and executive directors cast different numbers of votes reflecting their respective financial contributions. It is well known that a property of such weighted voting systems (other examples are the EU Council of Ministers, shareholders' meetings in joint stock companies) is that a member’s power - in the sense of its general ability to influence decisions - is not the same as its share of the votes. The system is designed to give power unequally to different members but its implementation might result in too much or too little inequality. The most important decisions require special majorities of 85% of the votes, giving the USA - with over 17 percent - an effective veto. This very high majority requirement has been criticised as both likely to make the decision making system too rigid and also to be damaging to American sovereignty by making it easier for others to block US proposals. When the Bretton Woods system was being planned in 1943, John Maynard Keynes warned of this. This paper uses game-theoretic measures of voting power to answer the following questions: 1. Is the inequality of voting power between countries a fair reflection of the differences in their respective contributions? 2. How does the size of the majority requirement employed affect the voting powers of the main contributors and the effectiveness of the IMF in being able to make decisions by majority voting? 3. How should the votes be weighted to give each country a given share of the power to influence decisions in general? The findings, using the voting weights for 1999, are that: (1) Countries' voting powers over ordinary decisions are much more unequal than their financial contributions; the power of the USA is much greater than its nominal 17% of the votes. (2) The effect of the special 85% majority requirement for major decisions is to severely limit the effectiveness of the decision-making system. (3) The use of the 85% majority requirement is counterproductive to the US pursuing an active role in the IMF by limiting its power to have its policies accepted. (4) The IMF should make all decisions by simple majority and scrap special majorities. That would make its democratic decision making system most effective. (5) The United States should support the use of simple majorities for all decisions if it wishes to increase its influence within a democratic IMF. (6) Votes of all members and executive directors should be reweighted in order to give the desired share of voting power to each country and director.