The package is a supplement to Dr. Michael Lustig's ESPIRiT package, available at http://www.eecs.berkeley.edu/~mlustig/Software.html. The main purpose function of the SP3 package is to extend the SPIRiT method to 3D. Here we focus on data acquired with stack of non-Cartesian 2D trajectories. To use this package, the ESPIRiT package must be downloaded and set in the path. Setup First download and setup the ESPIRiT package from the link above, then download SP3. Copy the m-files in @NUFFT to the @NUFFT of ESPIRiT/, and copy the m-file in utils/ to the utils/ in ESPIRiT/. Copy @SPIRiT3 to ESPIRiT/. Add ESPIRiT and all subdirectories to MATLAB search path. The example code and data provide a template of how to use the code.