There are numerous international conventions and agreements which cover MLA. In that sense, MLA’s primary basis is international agreements between states, both bilateral and multilateral. On a national scale, most countries have some sort of legislations on MLA, generally based on international agreements, to set out the national rules and standards. In most cases, not having legislation on MLA is not a basis to abstain from asking for the assistance of foreign authorities nor it is a basis to refuse to afford assistance to foreign interlocutors. However, it is strongly advised to have national legislation on MLA.
Most countries that have legislation on MLA in effect have separate legislations covering the issue. However, it is not necessary as there are numerous countries that cover MLA within their criminal or criminal procedure codes.
The absence of bilateral or multilateral agreements is generally not a basis to refuse demands of legal assistance as well. However, some countries require the existence of bilateral or multilateral agreements covering the issue, as per their national legislations.
In the event of the absence of bilateral or multilateral agreements, countries can afford assistance to each other on the basis of international customary law and the principle of reciprocity and comity. After all, the first examples of MLA were based on these fundamental ideas.