Past analyses of Atmospheric Fields variability over North America and surrounding areas have suggested the existence of strong signals of low frequency variations in interannual to interdecadal time scales. By analysing a 51-year (1958-1998) records of atmospherics fields derived from NCEP Reanalysis and other data, a look over the main features of its Climate Variability in the Inter- Americas Sea Region (IASR) is shown. Changes in the circulation modes in the middle 70s, related to a shrinking of Subtropical Ridge over the IASR, were detected and it may be linked to trends in ENSO conditions and some teleconnectives patterns such as the NAO and PNA. Besides, the nature of significant trends, observed in the atmospheric fields of different levels, is discussed suggesting the existence of a tropospheric warming in the IASR Regarding interannual variability, the influence of ENSO related patterns over the behaviour of the atmospheric circulations was analysed using the ENSO Index (EI). Winter patterns over the Western portions of the Region proved to be more sensitive to ENSO influence. However, analyses suggested an interdecadal variation in the ENSO influence over the Region that could be related with changes in the Climatic Background in the Pacific Ocean.