Beam intensity and position monitoring at synchrotrons has become more challenging as the technology of X-ray optics has been steadily improved: focusing down to the micron level is now routine, and the goal for the next few years is to operate at the 10nm scale. Beam movements result from vibrations and thermal drifts in the X-ray optical elements which are typically spread over a hundred meters length of the beamline. These movements must be monitored, and ideally compensated by feedback mechanisms with bandwidths of several kHz. We are developing thin (<100µm), position sensitive diamond devices which absorb <10% of the transmitted X-ray beam, generating electrical charge from the photoelectric absorption and Compton scattering processes. The induced signal currents are measured either with electrometers or using both wide-and narrow-band RF readout up to ~GHz frequencies. Difference-sum measurements of signals from segmented electrodes allow the determination of both beam intensity and position. Results already achieved with resolutions <20nm measured at the ESRF and DESY synchrotrons are presented. The nanosecond charge transit time in the diamond detectors and their excellent current source characteristics also allow for measurements of the X-ray parameters on a pulse by pulse basis, as required by the '4th generation' free electron laser sources such as the Linac Coherent Light Source at SLAC.