Coronal mass ejections (CMEs) hurl huge volumes of magnetized plasma into interplanetary space often referred to as ICMEs or ejecta. They are an important component of solar wind and can cause enhanced geomagnetic activity when they interact with the Earth’s magnetosphere. When the ejecta have an average speed greater than the upstream solar wind speed they create a shock. The large IMF variations due to interplanetary shocks cause depression in the cosmic ray intensity (CRI) called Forbush Decrease (FD). Large FDs caused by fast CMEs are specifically associated with energetic X-ray flares. In the present paper, the author has studied seven largest Forbush decrease events selected from Moscow Neutron Monitor Station during a period of twelve years (1996-2008), i.e., 23rd solar cycle. The analysis of CRI data with interplanetary magnetic field |B|, its southward component Bz, solar wind velocity, Kp and Dst indices shows that all the three phenomena- solar, interplanetary and geomagnetic are connected to FD. The relationship between interplanetary parameters and FDs is discussed in detail. Moreover the solar cycle effect is found to be slightly shifted for large FDs as the frequency of occurrence of major FD events is more in the descending phase of the solar cycle.