As of 19.00 on Sunday night up to 200 Jubilee and Northern Line maintenance staff staged a 24hr walk-out over a pay dispute.
From 17.00 on Monday, thousands of their colleagues (drivers, station staff and signallers) are staging a separate 24hr strike over plans to scrap 800 jobs in Underground ticket offices.
In addition, RMT & TSSA members start an indefinite overtime ban from midnight on Monday 6th September, which may lead to further staffing problems.
TfL have arranged "around a hundred extra buses, escorted bike rides, marshalled taxi ranks, and capacity for 10,000 more journeys on the river" to keep Londoners moving during the strikes. In addition, Volunteers will be positioned at Tube, bus and rail stations to assist commuters in their journeys.
Overground, Tramlink and DLR services are expected to operate as normal (with disruptions expected on stations which interchange with the Tube), and Londoners who cycle are encouraged to do so to get about.
For up-to-date information on how to get around, check www.tfl.gov.uk, which will be updated throughout the day.
Dan Milmo in The Guardian perhaps sums it up best:
"The London transport network faces waves of industrial unrest amid fears that more jobs and services will be cut under Boris Johnson's funding settlement with the government.
"Transport secretary Philip Hammond and Johnson, the London mayor, have identified the preservation of multibillion-pound upgrades to the tube system as a key priority. However, on the eve of a one-day walkout by tube workers over staff cuts, transport experts have warned that preserving the underground revamp will inevitably lead to deep cuts in Transport for London's operational budget – setting the mayor's TfL authority on a collision course with trade unions."
TfL have offered to resume talks at any point with the RMT and TSSA unions ahead of tonight's strike, but it would seem that these actions are likely to be the first of many threatened as cuts start to bit across the transport network, and money is ring-fenced for big-ticket items such as the Tube upgrades and CrossRail.
UPDATE 07.09.10: The BBC are running a live update feed here.