Shape Memory Alloys (SMAs) are a class of smart materials capable of undergoing reversible solid state phase transformations, enabling them to recover large deformations and produce significant mechanical work in compact volumes. These unique properties make SMAs particularly attractive for emerging applications in soft robotics, biomedical devices, aerospace systems, and other fields where silent operation, lightweight design, and high energy density are essential. Despite their promising attributes, SMA actuators face key limitations namely, restricted stroke to force trade offs and low actuation frequency due to slow thermal recovery hindering their broader adoption in dynamic and high performance systems. This thesis addresses these limitations through the development of novel actuator architectures, advanced thermomechanical modeling, and performance enhancing strategies focused on improving efficiency, responsiveness, and tunability. A comprehensive analytical model is developed to capture the full thermomechanical behavior of these actuators. The model refines classical SMA constitutive frameworks by introducing explicit phase boundaries between austenite, twinned martensite, and detwinned martensite, resolving ambiguities in intermediate phase transitions. Additionally, latent heat effects are incorporated into the thermal model to improve temperature prediction during phase changes. These formulations are validated experimentally using Ω-shaped kirigami actuators, demonstrating strong agreement between theoretical predictions and measured force temperature responses. Building on this modeling foundation, the thesis explores the working principles and fabrication techniques of kirigami-based SMA actuators. A flexure based bias spring mechanism is introduced to control deformation direction and improve stroke force trade offs. Parametric studies and experimental validation confirm that actuator performance can be accurately predicted using standalone SMA properties in conjunction with known spring stiffness. The importance of fabrication method is also emphasized; Water Jet Guided Laser Beam (WJGLB) cutting is shown to outperform conventional laser techniques by preserving microstructural integrity, minimizing surface oxidation, and enabling more consistent thermal and mechanical performance. To address the frequency bottleneck in SMA actuation, the thesis investigates a range of passive cooling strategies. Thin film coatings of thermally conductive metals are applied to SMA surfaces, accelerating heat dissipation without sacrificing flexibility. In addition, alternative geometries, specifically Twisted and Coiled Artificial Muscle (TCAM) SMA actuators, are introduced and modeled. These configurations increase actuator stiffness and output force while enabling faster thermal cycling. Finally, the thesis proposes a bistable actuator system composed of multiple SMA elements arranged to enable sequential activation. This architecture distributes the thermal recovery phase across modules, significantly reducing the overall actuation cycle time without requiring active cooling mechanisms. A functional prototype demonstrates the feasibility of this approach, offering a scalable solution for high frequency, high force actuation in compact systems. Collectively, the contributions of this work establish a new direction for the design and optimization of SMA-based actuators.