An act of the UK parliament which provides a legal framework for people whose capacity is impaired. It is meant to ensure that they participate as much as possible in any decisions made on their behalf, and that these are made in their best interests. It also allows people to plan ahead for a time in the future when they might lack the capacity, for any number of reasons, to make decisions for themselves. The MCA is supported by a detailed code of practice (‘the code’) which sets out best practice for professionals when treating patients who lack capacity. Dental care professionals have a duty to have regard to the code when necessary and failure to comply with it can also be used as evidence in court or tribunal proceedings. The MCA is underpinned by five principles that should guide dental care professionals and others involved in treating or caring for those whose capacity is impaired: a person must be assumed to have capacity unless it is established that he lacks capacity; a person is not to be treated as unable to make a decision unless all practicable steps to help him to do so have been taken without success; a person is not to be treated as unable to make a decision merely because he makes an unwise decision; an act done, or decision made, under the act for or on behalf of the person who lacks capacity must be done, or made, in his best interests. Before the act is done, or the decision is made, regard must be had as to whether the purpose for which it is needed can effectively be achieved in a way which is less restrictive of the person's rights and freedom of action. The act has been substantially amended by the Mental Health Act 2007.