Between 5pm on Thursday, April 28 and 12.25pm on Monday, May 2, a JCB 8026 excavator was taken from Pearie Law Wind Farm, in West Calder.
The 3.5 tonne piece of machinery is valued at around £30,000.
Anyone who saw a large piece of machinery being transported in the area between Thursday evening and Monday evening has been asked to contact Police Scotland on 101 quoting reference 1721 of 2 May. Alternatively, you can contact Crimestoppers anonymously on 0800 555 111.