Family therapy can involve any number of interested and invested parties in a family system and a single or team of therapists. Most importantly, attendance is limited to parties who are invested in the positive growth and change of the family system. This style of therapy is again collaborative and focuses on changing the system and its dynamics rather than change of any individuals in that system. This is appropriate when a family system has become ill and its persons and patterns are repeatedly harming each other and the system itself. Family Therapy is one of the most difficult areas in which to work due to competing needs, agendas, and styles of each family member. The most important requirements are investment and safety (an agreement to use the sessions and the discovered material only for positive ends.)