Over the last decade, the reach of the internet to the mobile platforms has redefined the usage of the mobile devices from voice-centric to data-centric. Parallel to this trend, location is becoming significantly more native to the mobile devices. This can be attributed mainly to the increasing prevalence of GPS-empowered handsets. Nowadays, Location-based Services (LBS) feature many useful consumer services like navigation, location-based search, and location-based advertising. With the increased integration of high-end GPS units in mobile devices, combined with the integration of orientation sensors like digital compasses and accelerometers, a new class of mobile Location-based Services (LBS) is emerging: the viewer-centric mobile services. With focus on viewer-centricity, viewer-centric mobile services aim at providing the user with information and services that are not only relevant to her current location, but also relevant to her field-of-view. Therefore, a viewer-centric service where a restaurant is located in her viewing range, what food menu it is offering etc., all by pointing the mobile device to scan the surrounding objects. The main goal of this thesis is to develop a framework for viewer-centric mobile services and a query model, with main focus on modeling viewer-centric queries from the GPS and orientation sensors existing in modern mobile devices. As these sensors, regardless of their fabrication quality, do suffer from runtime uncertainties, e.g. blockage of GPS signal by buildings, distortion of magnetic field due to nearby metallic structures, a key concept of the proposed framework, iVu.KOM, is to recognize the effects of such uncertainties on the overall accuracy of the modeled queries and to offer a means to correct the queries, when needed. As the view of the user is also affected by obstacles, e.g. buildings, that exist in the user's surrounding and limit the viewing range, the framework aims as well at efficient execution of the viewer-centric queries against the world geometry model. For this purpose, the proposed iVu query model suggests to include in the query result both the retrieved points of interest and a simplified description of the surrounding geometry. This query model allows executing the queries promptly on the client and with minimal need to contact the server, even when the visibility changes due to user's motion. To evaluate the feasibility of the proposed framework and model, a prototypical implementation of iVu.KOM was realized for a modern mobile platform featuring the required sen