"Black" cabs in Edinburgh (the same type used in London) are very roomy and can comfortably seat up to 5 people.  Some cabs are now available for 6 passengers.   You'll know if they are available if the "taxi" light above is on, to flag one down just wave or hold your arm up to attract the driver's attention.   All cabs can accomodate wheelchairs too.    Fares are metered within the city with additional charges to surrounding towns.   If you want to go further afield there are fixed fares which the driver can advise you of before you leave.

Late at night in the city centre it may be easier to head for a taxi rank.   There are marshalls on many ranks at the weekend to assist customers.   Some taxi drivers will refuse to let you on with food (pizza, fish and chips, burgers etc) and if you look in a very bad state (excessively drunk) they won't risk having you in the cab.  Should you be sick in the taxi there is a clean up charge of 21.60 pounds.   

All drivers are registered and licenced (as are the cabs) and should have their ID on display inside the cab.  On the whole drivers are very friendly and are extremely knowledgeable of the city so you'll never get a blank look once you give them an address or a hotel name.  Tip: Ask your cab driver for a card so you can call for a cab during busy spells or bad weather.   If you order a cab by phone this can add a little extra on to the price ( 80 pence ).  Specify if you need a cab for 6 or more passengers.   

Tipping is optional, 10-15% is fair but you are only expected to tip if you think the driver was helpful or friendly.  Taxi rates are increased very slightly in the evening and weekends.  At specific dates during the festive season (Christmas and  around New Year) the  prices are increased by about 25%

There are also private hire cars which must be pre-booked.  Many of these companies offer cars with additional capacity so are popular with groups needing more than 6 seats.

Taxis at the airport are available at the airport's taxi rank. Taxis can also be booked by phone in advance from one of the many taxi companies serving the airport .There is a pre-booked taxi pick-up point on the side of the multi-story car park just outside the terminal building.