The basic assumption of our daily work as lawyers is that generally, people will follow the terms of an agreement, and that compliance is the default mode of operation. A widespread normative aversion to intentionally breaking contracts is a fundamental societal assumption. This assumption informs our work as lawyers in negotiating and drafting agreements.
In US: must be an attorney licensed and in good standing in any state, territory or DC.
Outside US: must be a lawyer or equivalent (eg counselor, barrister, advocate, solicitor), duly educated and licensed/accredited and in good standing.
As a general rule, experienced and currently practicing lawyers are more likely to be admitted.