How much language competence do migrants need in order to integrate or become citizens? Many countries ask for a basic command, but what is a fair way to assess that level? Welcome to our special section exploring the complex issues that arise from testing requirements

The decision to make language ­ability a requirement in the immigration processes is not one to be taken lightly. In this focus on migration and language testing, supported by Cambridge Esol, we highlight some of the complexities that lie behind the apparently simple notion that new arrivals should demonstrate their ­language competency.

The contention that it is a good thing for migrants to be able to ­communicate in the language of their host community has widespread ­support, and migrants themselves are often very vocal in expressing this as their aim. Much more divisive are expectations about what level of ­language competence migrants should have and policies that require them to prove their ­ability before they are ­allowed to ­acquire rights and gain access to services or enter the host country.

In moving towards testing, policy–makers need to understand how ­language ­assessment works and how to design tests that return reliable ­results and are fair for the people ­taking them, but critics say in many cases that knowledge is lacking.

On these pages we have invited test development professionals and leading academics in the field to explain the challenging complexities of language testing. At stake are fundamental ­issues about the justice of testing, which critics argue are often ignored in public ­debates about control of migration, and the need for language testers to explain more clearly what role tests can play in both evaluating and developing ­language skills.

The content of the Migration and Language Testing section was produced by the Guardian Weekly to a brief agreed with Cambridge Esol. The costs were met by Cambridge Esol. All ­editorial ­content was commissioned and controlled by the Guardian Weekly.