Who is going on strike?
Rail, Maritime and Transport (RMT) union members at Network Rail and 13 train operators.
When are the strikes?
Tuesday, Thursday and Saturday.
How bad will the disruption be?
Fewer than one in five trains will run, and only on main lines and only for around 11 hours, starting later and finishing earlier.
Will there be strikes on the London Underground?
Yes. Members of the RMT and Unite will strike on Tuesday.
Are other unions involved in the dispute?
Yes. The Transport Salaried Staffs Association and the drivers union Aslef are also taking industrial action or balloting for strikes.
Why are the unions striking?
Talks between operators and the RMT continued into Monday afternoon, but the two sides could not reach a deal to resolve a row over pay and conditions.
Will there be more strikes after this week?
Yes. Members of Aslef on the Croydon Tramlink will stage a 48-hour walkout next week, and more strikes are likely if there is not a breakthrough.