Definitely the most popular way to come into Brighton without a car (and commute to and from London) - make sure to plan ahead and leave space for delays. When it's smooth, it's great, but when it's not, it can take hours!
The busiest line is Brighton to Victoria, running at least twice an hour all day, every day, until around midnight. The faster train clears the route in just over 50 minutes, while the milkround train takes about 70 minutes. You can also get straight to London Bridge and St Pancras in about 60 and 75 minutes respectively with almost the same frequency. This means you can actually get to Belgium in 3 hours from Brighton, or Paris in 3.5 hours, if you time it perfectly!
One thing to be aware of is that Southern Rail have a bit of a reputation for being unreliable (sometimes due to strikes) - most trains are fine, but if you want a bit of extra reassurance, the Gatwick Express trains are often a bit faster from Victoria and a bit more reliable.
There are often good prices on day travelcards to London, including train and tube for the day and Brighton is included in the PLUSBUS scheme, so you can often cover your train and bus in one go.
The best thing about arriving by train is how central the station is. It is 10 minutes from the city centre and about 15 from the seafront, all on a gentle downhill slope. You can also pick up buses to most of the surrounding area (including out to the South Downs or down to the Marina) or taxis from the front of the station.
Check out our quick Sightseeing guides for quick walking tours from the station!