EU law grants certain rights to passengers (i) departing from an airport within the EU on any airline or (ii) departing from an airport outside the EU for an airport within the EU if the airline is based in an EU state.
Airlines must offer the option of reimbursement or being rerouted in respect of cancelled flights, along with meals and telephone calls (and sometimes hotel accommodation). In addition, compensation must be paid unless the passenger is:
informed of the cancellation at least two weeks prior to departure
informed of the departure between one and two weeks prior to departure if a rerouted flight will result in no more than a four hour delay
informed of the departure between one and two weeks prior to departure if rerouting will result in no more than two hours delay
Airline passengers whose flights have been delayed by at least two hours are entitled to food and drink, access to phone calls and email, and accomodation for overnight delays. These must be arranged by the airline.
Delays which result in a passenger arriving at their destination at least three hours later than the original scheduled arrival time, are subject to compensation of between €250 and €600 (depending on the length of flight and the total delay).
If the reason for a delay or cancellation is outside of the control of the airline (eg due to bad weather or a security threat) compensation will generally not be payable.