The Romex system is a contract bridge bidding system designed by Mexican bridge expert George Rosenkranz. Key features of Romex are the multiple meanings attributed to certain bids, such as the dynamic one notrump and the Mexican two diamonds.

The dynamic one notrump opening indicates either:

The most common responses to the dynamic one notrump opening are:

Higher-level responses indicate control count.

A consequence of the use of the dynamic notrump is that the 1NT rebid by opener becomes wide-range (typically 12-16 hcp). With game invitational values or better, responder reacts to such a rebid with a 2♣ checkback convention to ask opener to further describe his hand.

This opening indicates one of four hands:

One-level and 2♣ openings are as per Standard American with 3+ minors and 5+ majors and limited by the failure to open one notrump.

Romex employs special asking bids in lieu of cuebidding, and for slam investigation.