Non-contact electrostatic imaging is an important mode of operation for scanning force microscopy (SFM). Electrostatic SFM has been used to image ultrathin liquid films, static charge distributions on insulating surfaces, spreading of liquid-crystal films, solvation of surface ions and surface potential variations of self-assembled molecular films, to list a few applications. For dynamic force microscopy in vacuum, it is important to minimize electrostatic interactions by nulling the tip-sample contact potential difference to better resolve atomic-scale structure. Various modes of SFM operation for non-contact electrostatic imaging are possible. One can drive the cantilever on or off resonance by applying an oscillating potential between the cantilever tip and the sample. One can combine off-resonance electrostatic excitation with on-resonance mechanical excitation. One can adjust the DC offset of the tip-sample potential to null the contact potential difference (Kelvin Probe operation). A report comparing experimental results for different electrostatic imaging modes has recently been published.@footnote 1@ The results of numerical simulations of the non-linear tip-sample interaction for the various electrostatic operation modes will be presented. The simulations include the cantilever dynamics and the response of the signal detection electronics, in addition to the tip-sample force. The advantages of the different operation modes will be analyzed, and the resolution limits for contact potential imaging will be discussed. @FootnoteText@ @footnote 1@ M. Luna, D. F. Ogletree and M. Salmeron, Nanotechnolgy 16, S1-7 (2005).