The aim of this work was to develop and validate simple, sensitive, accurate, and precise analytical methods for the analysis of two classes of drugs: 1. Antimicrobial drugs, namely; sofosbuvir, daclatasvir dihydrochloride, and ribavirin. 2. Anticancer drugs, namely; imatinib mesylate, sorafenib tosylate, and vandetanib. Another goal was to determine these drugs either in their raw materials, pharmaceutical formulations, and biological fluids with low cost depending on the availability of chemicals and equipments. The investigation utilizes the usefulness of high performance liquid chromatography as a powerful technique, and spectrofluorimetry, spectrophotometry, and chemometric techniques as simple and cost-effective techniques for the determination of the cited drugs. The thesis consists of four parts: Part I: Literature review of the studied drugs Part II: Spectroscopic method This part is divided into four sections Section A: Utility of Cremophor RH 40 as a Micellar Improvement for Spectrofluorimetric Estimation of Sorafenib in Pure Form, Commercial Preparation, and Human Plasma In this section; a novel method was successfully developed for the determination of sorafenib in pure form using a spectrofluorimetric method and utilizing cremophor RH40 as a fluorescence enhancer. A linear fluorimetric calibration curve was obtained in a concentration range (5-600 ng/mL). The method was successfully applied for the determination of sorafenib in pure form, pharmaceutical formulation, and human plasma. All results obtained were compared with those of the reported method, where no significant difference was observed. Section B: Spectrofluorimetric Determination of Imatinib in Pure Form, Pharmaceutical Formulation, Spiked Human Plasma, and Spiked Human Urine. In this section; a micellar medium of carboxymethyl cellulose (CMC) was used to enhance the fluorescence of anticancer imatinib drug. A linear fluorimetric calibration curve was obtained in a concentration range (4-900 ng/mL). All results obtained were compared with those of the reported method, where no significant difference was observed. Section C: Six Sequential Spectrophotometric Methods for Simultaneous Determination of Antiviral Drugs Ribavirin, Sofosbuvir, and Daclatasvir In this section; zero order direct, ratio difference, successive ratio derivative, constant center, iso absorptive, and mean center of the ratio spectra methods were used for the simultaneous determination of ribavirin, sofosbuvir and daclatasvir were described. The methods were successfully applied for the determination of the antiviral drugs in pure form, their pharmaceutical formulation, human plasma, and urine. All results were compared with those of reported method and no significant difference was observed. Section D: Extended Derivative Ratio Method for Simultaneous Determination of Ribavirin, Daclatasvir, Sofosbuvir and Sorafenib In this section; an extended derivative ratio method for the simultaneous determination of RIB, DAC, SOF, and SOR was described. The proposed method was successfully applied for the determination of each drug in pure form, pharmaceutical formulations, human plasma, and urine. All results obtained were compared with the reported method. Part III: Chemometric method This part includes one section Section A: Chemometric Methods for Simultaneous Determination of Ribavirin, Daclatasvir, Sofosbuvir and Sorafenib In this section; chemometric methods were used to analyse RIB, DAC, SOF, and SOR mixture. Multivariate calibration methods are utilized in spectral analysis improving the precision and predictive ability of these methods. Part IV: High performance liquid chromatographic method This part is divided into three sections Section A: HPLC Method for Simultaneous Determination of Sofosbuvir and Daclatasvir In this section; a simple, selective, and sensitive LC-UV method for the quantitative determination of SOF and DAC. The optimum conditions for the separation process were determined. anonyxTM C8 monolithic (100 × 4.6mm (i.d.) analytical column as a stationary phase. The mobile phase consisted of 0.1M sodium dodecyl sulfate (SDS) solution containing 20% (V/V) n-propanolol and 0.3% (V/V)triethylamine (pH 6.5) with effluent flow rate 0.5 ml/min and UV detection at 226 nm. Section B: HPLC Method for Simultaneous Determination of Sofosbuvir and Ribavirin In this section; a simple, selective, and sensitive LC-UV method for the quantitative determination of SOF and RIB. The optimum conditions for the separation process were determined. Nucleosil 100-5 phenyl column (250 × 4.6mm, 5 µm ) as a stationary phase. Sodium dodecyl sulphate solution (0.05 M, pH 7.0) containing triethylamine (0.3%) and n-butanol (10%) was used as a mobile phase with 1.2 mLmin-1 flow rate and 215 nm detection wavelength. Section C: Green Micellar HPLC-UV Method for Determination of Vandetanib This section comprises a simple sensitive HPLC-UV method for the quantitative determination of vandetanib. The optimum conditions were determined.