Adlayer structures of Cl and Br, and the formation of AgBr bulk layers on Ag(100) surface were investigated using in situ scanning tunneling microscopy (STM) in solution and ex situ low-energy electron diffraction (LEED) in ultrahigh vacuum (UHV). In situ STM clearly showed that adsorbed Cl and Br monolayers possess a c( 2 x 2) structure on Ag(100) in acidic solutions. Monoatomic steps were observed to run parallel to the <001> direction rotated by 45degrees with respect to the atomic rows of the Ag substrate. Ex situ LEED showed a clear pattern corresponding to the c( 2 3 2) structure in UHV after emersion of the sample from solution. At potentials for the formation of bulk AgBr layers, AgBr(100) layers grew epitaxially on Ag(100). On the Ag(100) surface, both Ag and Br ions in the topmost layer of the bulk AgBr were clearly observed by in situ STM. The LEED pattern showed a c( 2 x 2) crystallographic arrangement for the bulk AgBr(100) formed on Ag(100).