Cancer is a worldwide severe health issue, and its (colorectal and lung cancer) incidence is increasing continuously in young adults. However, therapeutic advances have decreased the mortality rate in some cancer patients but not in all. For example, immune checkpoint blockers or inhibitors (ICBs or ICIs) are the most recent cancer immunotherapeutic agents with demonstrated increased patient survival rates than other standard cancer therapies. However, they are very costly and exert serious side effects, including the development of autoimmune diseases (AIDs) and secondary tumors. Furthermore, ICIs work effectively in immunologically hot tumors with high tumor-infiltrating lymphocytes (TILs) and expressing high levels of immune checkpoints, such as PD-L1. They are ineffective in cold tumors with immunosuppressive tumor immune microenvironment (TIME). Oncolytic viruses (OVs) comprising oncolytic viral therapy (OVT) have been known for over 100 years. In this time frame, they have been genetically modified according to the tumor type, including their TIME, and optimized for their delivery and effective antitumor action. As cancer is a disease of dysregulated immune response generating a tumor-supportive TIME depending on the cancer type and its site of origin, therefore it is critical to understand TIME for better OVTs. Therefore, the current chapter is focused on the TIME and its understanding of better OVTs for different solid cancers.