LY2062430 (solanezumab) is a humanized anti-A Beta peptide immunoglobulin G-1 (IgG1) monoclonal antibody being developed for the treatment of AD. The primary hypothesis being tested is that LY2062430 will slow cognitive and functional decline in AD as compared with placebo. Each patient's participation will last approximately 19 months. Patients taking approved AD medications may participate in this study and continue taking these medications during the study.