In this thesis we study non-relativistic, low-energy, s-wave scattering in a four-body spin-1/2 fermion system. The scattering is caused by an attractive twoermion contact interaction which is capable of producing a weakly bound state known as a dimer. This fourermion system is used to study the scattering of a two-dimer system. Using Hybrid Monte Carlo methods we compute the ground state energies of the system on a lattice. Luscher’s finite-volume formula and the Effective Range Expansion are used to calculate the dimer-dimer scattering length add and effective range rdd in terms of the fermionermion scattering length aff. Using these techniques we obtain the values add=aff = 0:60 +/- 0:04 and rdd=aff = 3:2 +/- 0:5. This scattering length shows excellent agreement with the numerous values in the literature. We also compare this effective range with the only currently known value in the literature.