Lithographic apparatus

A lithographic apparatus comprising:

• a substrate table comprising a holder configured to hold a substrate in a holding plane;
• a projection system configured to project, when the substrate table is positioned in an exposure area, a patterned radiation beam onto a target portion of the substrate;
• a substantially vibration isolated frame supporting the projection system,
• a substrate table position measurement system configured to measure a position of the substrate table, wherein said substrate table position measurement system comprises
• a substrate table reference element arranged on the substrate table, and
• a first sensor head configured to determine a position of the first sensor head with respect to the substrate table reference element, wherein said substrate table reference element extends in a measurement plane substantially parallel to the holding plane, and wherein said holding plane is arranged at one side of the measurement plane and the first sensor head is arranged, when the substrate table is in the exposure position, at an opposite side of the measurement plane,
• a sensor frame mounted on a sub-frame of the lithographic apparatus and wherein the first sensor head is mounted on the sensor frame;
• a projection system position measurement system configured to measure a position of the projection system, the projection system position measurement system comprising a projection system reference element and a sensor assembly to determine a position of the sensor assembly with respect to the projection system reference elements, and
• wherein one of the sensor assembly and the projection system reference element is mounted on the projection system, and the other one of the sensor assembly and the projection system reference element is mounted on the sensor frame.