Before you start

California residency
Proof of identity and lawful presence, or AB 60 alternative documents
A Social Security number, or a declaration that you have none
One California residency document; two for a REAL ID
Separate Mexican auto insurance if you intend to drive south

Step-by-step

1
Book the DMV appointment before you land
The ten-day deadline collides with appointment availability. San Diego coastal offices are the busiest; El Cajon, Escondido and Chula Vista are often sooner.
OnlineWho: YouBefore arrival
2
Pass the knowledge test and get an instruction permit
California has no exchange arrangement with any country, so you are treated as a new driver regardless of experience. The permit is required before the drive test.
In personWho: You
3
Take the behind-the-wheel drive test
You supply a registered, insured vehicle and a licensed accompanying driver. Driving schools rent both together, which for a newcomer without a car is usually the only route.
In personWho: You
4
Buy Mexican insurance before driving south — every time
US auto policies do not provide liability cover in Mexico. Driving there without Mexican liability insurance can mean detention after even a minor collision, because liability is treated as a criminal matter until resolved. Short-term policies are sold online and at the border for a few dollars a day.
OnlineWho: You
5
Check border wait times before returning
CBP publishes live northbound wait times, and apps surface them. A three-hour queue at San Ysidro on a Sunday evening is normal; Otay Mesa is often faster. Plan the return, not just the trip.
Mobile appWho: You
6
Consider not driving across at all
Walking across at San Ysidro and using the Trolley on the US side avoids the vehicle queue, Mexican insurance and parking entirely. For a day trip it is usually the better choice, and it is what most regular crossers do.
In personWho: You

Documents you’ll need

Foreign driver licence
Passport, visa and I-94 as identity and lawful-presence documents
Social Security number, or a declaration of ineligibility
One California residency document, or two for a REAL ID
Mexican auto insurance policy, if driving south

Things most newcomers don’t know

Your US car insurance is worthless in Mexico, and the consequence is not financial.

Mexico treats liability for a collision as a criminal matter until it is settled, and without recognised Mexican liability insurance a driver can be detained after even a minor accident. US policies — including those that mention 'Mexico coverage' for physical damage — generally do not satisfy the liability requirement. Buy a Mexican policy for every trip; it costs a few dollars a day.

Source: US Department of State — driving in Mexico

California waives testing for no country whatsoever.

Texas waives both exams for licences from France, Germany, South Korea, the UAE and Taiwan; Florida requires only a vision and hearing test. California waives nothing for anyone, so an experienced foreign driver starts from a knowledge test and an instruction permit.

Source: California DMV — requirements for a California driver licence

Otay Mesa is often much faster than San Ysidro.

San Ysidro is the busiest crossing in the hemisphere and its northbound queue is the default assumption. Otay Mesa, twenty minutes east, frequently clears far quicker, and the difference on a Sunday evening can be two hours. Check both on the CBP wait-time feed rather than defaulting.

Source: US Customs and Border Protection — border wait times

The Trolley reaching the border is genuinely unusual.

The Blue Line terminates at San Ysidro, so you can travel from UC San Diego to an international frontier on a light rail fare, walk across, and be in central Tijuana in minutes. Almost no US transit system does this, and it makes a car unnecessary for the crossing itself.

Source: San Diego Metropolitan Transit System

Common mistakes to avoid

Driving into Mexico on a US insurance policy, which does not cover liability there.
Assuming your foreign licence can be exchanged — California has no such arrangement.
Arriving without a DMV appointment inside the ten-day deadline.
Defaulting to San Ysidro on the return without checking Otay Mesa's wait time.
Turning up to the drive test without a registered, insured vehicle and a licensed accompanying driver.

Some of this may be out of date. Spotted something inaccurate? Help us keep it right for the next newcomer.