the quadrotor is a type of unmanned aerial vehicles (uavs) which is gaining popularity over the past few years for its potential applications. quadrotor uavs are used, for instance, for surveillance, search and rescue missions, monuments inspection, and aerial photography. the crucial step towards a reliable application is the development of efficient attitude esti- mation and control algorithms. the primary focus of this thesis consists in investigating various attitude control techniques and their applications. a nonlinear attitude estimator and a pd-like controller have been successfully implemented on a quadrotor uav. however, the stability proof of the attitude observer/controller com- bination is not obvious as the system is nonlinear. to solve this problem, an attitude controller directly relying on inertial vector measurements and angular velocity has been proposed. some practical methods such as filtering and vector decoupling were developed and discussed. moreover, an inertial measurements based velocity-free attitude controller has been designed. finally, real-time implementation has been conducted on a small-scale low-cost quadrotor uav. experimental results have been carried out to show the effectiveness of the proposed controllers and some experimental problems and further approaches of the velocity-free controller are discussed.