We study voting situations in which the number of candidates to be elected is given by a quota. Some of the most well-known rules, such as approval or plurality, do not impose any restriction on the number of possible winners to select. However, there are many cases (the election of a Prime Minister, for example) in which such a restriction exists. We develop a framework to analyze these cases, in which the voting scheme depends both on the votes voters may cast and on the quota to fulfill. As a result, we identify the family of voting systems that are fair (satisfy support anonymity and strong candidate monotonicity) and stable (satisfy consistency).