The paper presents a technique for constructing one-loop amplitudes in gauge theories using unitarity and collinear limits. Specifically, it focuses on the $N = 4$ supersymmetric Yang-Mills theory and derives the one-loop contribution to amplitudes for $n$ gluon scattering with the helicity configuration of the Parke-Taylor tree amplitudes. The authors prove the correctness of their ansatz for $N = 4$ amplitudes using general properties of relevant one-loop $n$-point integrals. They also provide "splitting amplitudes" that govern the collinear behavior of one-loop helicity amplitudes in gauge theories. The paper reviews known results for tree and one-loop amplitudes, describes the collinear behavior required for a general amplitude, and constructs an ansatz for the leading-color part of the $N = 4$ super-Yang-Mills $n$-point MHV amplitude. It then calculates the cuts for this amplitude and shows that the ansatz has the correct cuts. Finally, it proves the correctness of the ansatz using the structure of the loop integrals and provides a general formula for subleading-color contributions to $n$-gluon amplitudes.The paper presents a technique for constructing one-loop amplitudes in gauge theories using unitarity and collinear limits. Specifically, it focuses on the $N = 4$ supersymmetric Yang-Mills theory and derives the one-loop contribution to amplitudes for $n$ gluon scattering with the helicity configuration of the Parke-Taylor tree amplitudes. The authors prove the correctness of their ansatz for $N = 4$ amplitudes using general properties of relevant one-loop $n$-point integrals. They also provide "splitting amplitudes" that govern the collinear behavior of one-loop helicity amplitudes in gauge theories. The paper reviews known results for tree and one-loop amplitudes, describes the collinear behavior required for a general amplitude, and constructs an ansatz for the leading-color part of the $N = 4$ super-Yang-Mills $n$-point MHV amplitude. It then calculates the cuts for this amplitude and shows that the ansatz has the correct cuts. Finally, it proves the correctness of the ansatz using the structure of the loop integrals and provides a general formula for subleading-color contributions to $n$-gluon amplitudes.