The Lotus 9 or more properly Lotus Mark IX, was an aluminium-bodied sports race car manufactured by Lotus Engineering Ltd. and was closely related to the type 8 of which only about seven cars were made. These cars were largely based on the innovative space frame of the Lotus Mark VI. The highly aerodynamic bodies were designed by Frank Costin and constructed by Williams & Pritchard Coachworks.

 During this early era of 1954-1955, Lotus Engineering was still a fledgling company, and cars were delivered in different states of completion on special orders. Similar to the Mk 8 the Mk 9 was available in various configurations and different engines including the 1500 cc MG, 1500 cc Connaught and 2 liter Bristol were fitted, however, the Mk9 designation is most often powered by the 1100 cc Coventry Climax engine. Apparently two models of Mk 9 were offered – the “Club” and the “Le Mans,” the latter of which had larger drum brakes fitted.

Compared to the Mk 8, the Mk 9 was shortened somewhat to a wheelbase of 7' 3.5", and the body itself was about two feet shorter than that of the Mk 8. A total of about thirty of the Mk 9 sports racing cars were produced in various forms and these were successfully raced in both Europe and the US. The first two examples of the Mk 9 were apparently delivered to the US with the 1100 cc Coventry Climax engine to compete in the 1955 running of the 12 Hours of Sebring race and were beaten by a Porsche Spyder. These cars were actually entered as Lotus Mk 8 models in the G class by Frank Miller of Larchmont, NY and by Bobby Burns and Norman J. Scott of Houston TX in respectively cars number 78 and 79. The Lotus works entered at least one Mk 9 in the Le Mans 24 hour race in 1955 driven by Chapman, which may have been equipped with disc brakes, however the car was disqualified apparently due to his reversing the car to reenter the race track after going off course.