Knowledge of reservoir properties, such as reservoir permeability, is critical for hydraulic fracture stimulation design in multi-fractured horizontal wells (MFHWs). In practice, a wide range of methods can be used to obtain reservoir parameters. However, most methods, such as openhole logs, core analysis, rate-transient analysis (RTA), and conventional diagnostic fracture injection tests (DFITs), have important limitations regarding their accuracy, reliability, time- and cost-efficiency. The DFIT flowback analysis (DFIT-FBA) method, which involves the sequence of pump-in/flowback, is a fast alternative to the pump-in/falloff (conventional) DFIT for estimating minimum in-situ stress and reservoir pressure. However, improvements in both the design and analysis of DFIT-FBA are required to improve its reliability and practical application. An important limitation of this method is that, because the properties of the fracture are unknown, reservoir permeability cannot be estimated directly; only well productivity index has been reported in previous DFIT-FBA studies. Another promising fracture/reservoir characterization method is the post-fracture pressure decay (PFPD) technique. With this method, the pressure falloff following the hydraulic fracture stimulation treatment of an individual stage of a MFHW is analyzed. Methods to analyze PFPD data are in their infancy, and further improvements in the analysis methods are required; previously-applied analysis methods have either oversimplified the mechanisms behind PFPD, or have erroneously applied conventional DFIT analysis techniques. However, initial field studies have demonstrated that the technique provides a cost-effective tool for stage-by-stage comparison of reservoir/fracture properties and completion design. Therefore, the overall goal of this dissertation is to improve the design and analysis of DFIT-FBA and interpretation of PFPD data, and to integrate the DFIT-FBA method and PFPD techniques for more confident stage-by-stage evaluation for MFHWs. An analytical model is first developed for the DFIT-FBA method, which allows for improved design and analysis of a DFIT-FBA test, fault identification (in order to evaluate the risk of induced seismicity), and reservoir permeability estimation. Moreover, new corrections are introduced to the DFIT-FBA method to account for perforation friction, tortuosity, and wellbore unloading to improve the accuracy of the estimated parameters in cemented horizontal wells. Practical applications of DFIT-FBA to hydraulic fracturing design and reservoir characterization are demonstrated by using multiple DFIT-FBA tests performed at different points along the lateral section of a horizontal well, and also at the toe of different wells. Finally, a new PFPD analysis method is developed to incorporate the key mechanisms occurring during the pressure falloff after individual-stage hydraulic fracturing. To account for the variation of reservoir properties along the horizontal well, the PFPD model is integrated with DFIT-FBA tests, performed at several points along the lateral, to obtain a reliable stage-by-stage hydraulic fracture and reservoir characterization approach. Practical application of the proposed integrated approach is demonstrated using PFPD and DFIT-FBA data from a horizontal well completed in an unconventional reservoir. With the proposed integrated methods, reservoir/hydraulic fracture properties along the length of horizontal wells can be derived, and the presence of faults and pre-existing fractures can be identified. Along-well reservoir/fracture characterization makes it possible to achieve equal or greater hydrocarbon recovery using fewer wells and hydraulic fracture stages per well. Therefore, not only will revenues be increased, but the environmental impact of unconventional reservoir exploitation, including resources used, risk of induced seismicity, greenhouse gas emissions, and surface footprint associated with drilling/completion activities, will be mitigated. It should be noted that the technologies advanced in this thesis are equally applicable to clean energy pathways (CEPs), such as geologic sequestration of carbon dioxide, hydrogen storage and production, and geothermal energy production. For example, DFIT-FBA can be used to quickly evaluate caprock integrity for gas storage applications, and PFPD can be used for evaluating CEPs that require multi-stage fracturing, such as enhanced geothermal systems.