# EI Library Reference

Version 3.5.5.1

The `ei` library is a `C` interface library for communication with `Erlang`.

| By default, the `ei` library is only guaranteed to be compatible with other Erlang/OTP components from the same release as the `ei` library itself. See the documentation of the ei_set_compat_rel() function on how to communicate with Erlang/OTP components from earlier releases.

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