Jersey and Guernsey both have airports with regular flights from London (Heathrow, Gatwick, London City, Stansted), Bristol, Southampton, Manchester, Edinburgh, and a number of other UK regional airports. Flight times from London are around 45 minutes. Aurigny Air Services connects Guernsey to Alderney and also operates from London Gatwick. Blue Islands operates smaller inter-island routes.
The main ferry operator is Condor Ferries, running from Poole and Portsmouth to both Jersey and Guernsey. The Poole crossing takes around 3 hours to Guernsey and 4.5 hours to Jersey on the fast ferry; overnight conventional ferries from Portsmouth take longer. Condor also runs a seasonal service from Weymouth. Book ahead in summer — car spaces on ferries fill up well in advance.
From France, ferries run from St Malo to Jersey and Guernsey; the crossing from St Malo to Jersey takes about 1 hour 10 minutes on the fast service. Manche Iles Express operates seasonal routes from Granville and Carteret in Normandy to Jersey and Guernsey.
There is no direct ferry from the UK mainland to Alderney, Sark, or Herm — you need to go via Guernsey.