The aim of the Super-MuSR project is to make maximum scientific use of the muons delivered to the MuSR arm of the ISIS muon facility. It will maximise the counting rate by doubling the detector solid angle coverage, increasing the number of detectors, and improving the counting rate of each detector. The beamline will provide switchable pulse slicing and spin rotation to improve the time resolution and make it useful for higher transverse field experiments. Here we report the scientific design of the Super-MuSR spectrometer and beamline.