DNA-drug interactions play a major role in therapeutics, diagnostics, forensics and imaging. Drugs bind to DNA in several ways based on the mode of interaction and they alter protein-DNA interactions or breaks/cleaves DNA that can lead to the cure of the disease. The major goal of the research carried out in this thesis is to develop novel optical spectroscopic tools that can differentiate Drug-DNA binding interactions mode whether its intercalation or minor-groove binding. To achieve this goal, we developed two-photon absorption (2PA) cross-section based technique to differentiate between Drug-DNA binding modes. The investigations were carried out on two drug molecules, DAPI and Thiazole Orange (ThO) binding to Salmon Sperm-DNA and Calf Thymus-DNA. DAPI binds to the DNA via minor-groove while ThO intercalates with DNA. Relative 2PA cross-section studies have shown about 3-fold enhancement for DAPI whereas ThO has shown no enhancement. These results confirmed our hypothesis. To further establish this method, studies were carried out using two more drug molecules, Netropsin and Doxorubicin with Salmon Sperm-DNA. Netropsin is a non-fluorescent drug that required a marker to read its binding interaction with DNA. Two types of markers have been used, Hoechst-33258 was used as minor-groove marker and Thioflavine T as intercalator. Doxorubicin drug is fluorescent and the binding results via the 2PA cross-sections have shown a slight decrease in 2PA-fluorescence, suggesting the intercalation binding mode with DNA.