The purpose of this report is to analyze the current methods of data integration in Computer-Assisted Neurosurgery applications. Neurological studies require the integration of anatomical data registered with CT Computed Tomography, MRI Magnetic Resonance and MRA Magnetic Resonance Angiography with functional data from Nuclear Tomographies, PET and SPECT along with fMRI Functional Magnetic Resonance and MEG Magnetoencelography. The first section of the document presents the physical model corresponding to the human brain, it describes the anatomy, the physiology and the pathologies that need the assistance of imaging modalities. The second section analyzes the type of data provided by the devices above enumerated, their values, type and range, the physical properties that they measure and their resolution. The impact of the registration on the patients is also evaluated taking into account the invasivity of the technique and its harmfulness. The third and the fourth sections focus at the integration itself. First, a general overview of the integration process is given. Next, different integration strategies are presented and compared. The fifth section addresses the modelling of integrated data. In the sixth section, the error of each step of the integration is analyzed. Finally, several strategies for the joint visualization of several data types are discussed. In the conclusions, a global evaluation of the different methods is presented, outlining their lacks and their advantages.