Sometimes called guardianship (depending on the state), a conservatorship is a legal arrangement whereby a conservator (or guardian) is appointed to make decisions on the incapacitated person's, behalf when they are found unable to manage daily life without being a danger to themselves or others. 

Conservatorship mostly deals with the management of the conservatee's finances, whereas guardianship deals with everyday care, such as help around the home, with medical care, etc. Britney Spears's conservatorship allows for both.

There are an estimated 1.5 million adults under guardianship in the U.S

• If you want to understand the modern conservatorship, you have to go back in time—at least half a millennium: these provisions go back to medieval England, to when the Crown took over the estates of noblemen who were unable to manage them.
• Conservatorships have changed in scope over the years. Whereas they have historically been all-encompassing more limited conservatorships are becoming an option.
• Conservatorships aren't necessarily easy to obtain. In general, since the late 1960s, it has become more difficult to commit someone against their will.