Mobile devices such as phones and tablets have become the most prevalent AR devices and are applied in various domains, including architecture, entertainment, and education. However, due to device-specific characteristics, designing and evaluating handheld AR interactions can be especially challenging as handheld AR displays provide 1) limited input options, 2) a narrow camera field of view, and 3) restricted context awareness. To address these challenges with design recommendations and research implications, the dissertation follows a mixed-methods approach with three research questions (RQs): On the one hand, specific aspects of fundamental 3D object manipulation tasks (RQ1) and awareness and discoverability (RQ2) are explored and evaluated in controlled lab studies. For increased ecological validity, the developed interaction concepts are also investigated in public interactive exhibitions. These studies then inform the creation of a framework for designing and evaluating handheld AR experiences using VR simulations of the interaction context (RQ3).