In prestressed concrete girders, the end-regions are often susceptible to high internal forces induced by prestressing, resulting in crack propagation. Resisting these forces necessitates a substantial amount of reinforcing steel, leading to complicated design and congested formwork. Despite this reinforcement, cracking due to prestressing still frequently occurs. Moreover, girder end-regions are susceptible to corrosive environments, posing a significant concern due to their correlation with sudden and catastrophic failure types. Ultra-High-Performance Concrete (UHPC) exhibits exceptional mechanical strength and durability, making it a promising material for addressing issues in prestressed applications. However, UHPC is a much higher-priced material than conventional concrete, making monolithic UHPC construction substantially more expensive. An alternative approach involves implementing UHPC selectively in sections of a girder, creating a composite member rather than a fully monolithic one, offering a more cost-efficient solution for prestressed concrete girders. This concept, defined as a hybrid girder, encompasses conventional prestressed concrete girder design for most of the member, except for the end-regions, where UHPC replaces both the conventional concrete and internal reinforcement. The primary concerns surrounding this concept relate to ensuring efficient construction and maintaining continuity between the different concrete types, facilitating homogenous behavior. This research investigated various interface designs for achieving adequate stress transfer in hybrid girder design while also having evaluated the constructability and load-response of these hybrid girders. The research project is comprised of two main components: a small-scale program that characterized seven different interface methods and a large-scale hybrid girder testing program that used the four top-performing interfaces. The findings of this study indicated that the hybrid girders concept is plausible for construction, interface continuity, and predictability of load-response. The performance of the interface depends on texture shape, size, pattern, and casting method. Simultaneously cast concretes with a similar rheology and trapezoidal-shaped cold-joint textures demonstrated enhanced performance. The shear testing of hybrid girders consistently exhibited web-crushing failure. An assessment of the hybrid girder testing considered existing shear calculation methodologies and revealed that accurate capacity estimation can be achieved using existing approaches. Empirical equations from the ACI 318 Detailed Method and strut-and-tie modeling with prescribed amendments provide precise lower and upper bounds for hybrid girder capacity, regardless of the selected interface design. Overall, the concept can offer a cost-effective solution, combining the strength and durability of UHPC in critical end-regions. The research underscored the practicality of this concept and offers a design procedure for hybrid girders.