Well trajectory design and optimization are essential parts in well planning before drilling. The main objective of the design is to find an optimal trajectory for efficient and safe drilling. Meanwhile, the anticollision of well trajectory must be considered with offset wells in the same area. In general, optimal wellbore trajectory design includes some essential criteria, for example, shortest possible path, minimum tortuosity, collision avoidance, and most extended possible contact with the reservoir. This article presents a central part of plan phase represented by a trajectory planning and optimization module with a focus on anticollision design. The trajectory is optimized based either on minimization of wellbore length and dogleg severity or on the maximization of well-reservoir contact subject to strict anticollision constraint and other associated constraints or their combinations to some extent. The anticollision model considers industry standard bit error sources and their interactions and propagation along the well trajectory, and results in the separation factor as an constraint for trajectory optimization. The introduction of anticollision models to the trajectory optimization techniques has real potential in drilling design. Besides saving time and effort by providing engineers with multiple options, the well design with anticollision considerations ensures the well path safety while searching for optimal well trajectory. The presented work has a good potential in well planning as a viable method to keep drilling operations’ safe and efficient.