In this talk, we introduce recent Sun-Earth connection studies which have been done in solar and space weather research group at KASI. In a series of papers, we have examined the physical characteristics of geoeffective halo CMEs that produced geomagnetic storms. First, we investigated the probability of geoeffective CMEs depending on its solar surface location and speed using SOHO/LASCO CMEs from 1997 to 2003. Second, we examined the relationship between several CME physical parameters (e.g., earthward direction, density, mass, location) and geomagnetic storms for very fast halo CMEs (VCME > 1300 km/s). In particular, we suggested a new earthward direction parameter that is defined as a ratio, the shorter front from the solar center to the longer one. Third, we examined the relationship between the field orientation in a CME source region and a geomagnetic storm using a coronal flux rope model as well as its dependence on ICME classification (magnetic cloud or ejecta). Major results are as follows. 1) The most probable areas whose geoeffectiveness fraction is larger than the mean probability (0.4), are 0<L<30 for slower speed CMEs (<800km/s), and 30<L<60 for faster CMEs (>800 km/s). 2) The CME direction has much better correlations with the Dst index than other parameters for very fast halo CMEs. 3) The relationship between the field orientation and the geomagnetic storm for magnetic cloud is much better than that for ejecta, implying that the field orientation of the magnetic clouds is well conserved through the heliosphere. We also briefly introduce several ongoing studies: (1) earthward direction as an important geoeffective parameter, (2) solar wind effect on the propagation of IP shocks, and (3) satellite drag effect during strong solar/geomagnetic activities and the comparison between the drag derived density and the MSIS-90 model. Finally, we present some future plans in the Sun-Earth connection field.