This dissertation addresses the signal-in-space integrity monitoring of the Local Area Augmentation System. The theoretical basis and the system architecture of the integrity monitoring are described. The performance of the baseline protection level algorithms defined in the "Minimum Aviation System Performance Standards for The Local Area Augmentation System" is verified by both theoretical analysis and computer simulation. It is shown that the underlying assumptions used in calculating the protection levels do not take into account the effect of the ground processing function. A modification to the baseline algorithms is presented. Procedures in verifying the algorithms along with other ground processing functions and/or with any number of reference receivers are demonstrated. Finally, improvements to the algorithms are discussed.