Some Magic Smoke managed to escape when he connected his 5V Arduino directly to the 3.3V ESP8266, but at least it was a fairly cheap mistake and he had spares on hand to get the project completed ...

The module requires both a USB interface and level shifter to interface the 2.8V levels of the module to the 5V Arduino Uno.

There is a level shifter so a 5v (Arduino UNO, etc) or a 3.3v (Arduino Zero, Raspberry Pi, etc.) micro controller can be used. Both can work simultaneously.