Withdrawal from a partnership can either be voluntary or involuntary.
A voluntary withdrawal means that the business partner has willingly decided to leave the partnership for one reason or another. For example, a common reason why a business partner might withdraw from a partnership is because they are retiring. In this case the withdrawing partner serves the notice on the partnership.
An involuntary withdrawal is served when the majority of the parties in a business partnership collectively decide that one partner should be removed from the partnership. This could be for any number of reasons, such as that the partner has passed away, was criminally convicted, or is found to be incompetent. In this case the remaining partners serve the notice on the withdrawing partner or the withdrawing partner's estate or legal representative.