Wireless sensor networks (WSNs) are being extensively deployed today in various monitoring and control applications by enabling rapid deployments at low cost and with high flexibility. However, high-level software development is still one of the major challenges to wide-spread WSN adoption. The success of high-level programming approaches in WSNs is heavily dependent on factors such as ease of programming, code well-structuring, degree of code reusability, required software development effort and the ability to tune the sensor software for a particular application. Component-based programming has been recognized as an effective approach to satisfy such requirements. However, most of the componentization efforts in WSNs were ineffective due to various reasons, such as high resource demand or limited scope of use. In this article, we present Remora, a novel component-based approach to overcome the hurdles of WSN software implementation and configuration. Remora offers a well-structured programming paradigm that fits very well with resource limitations of embedded systems, including WSNs. Furthermore, the special attention to event handling in Remora makes our proposal more practical for embedded applications, which are inherently event-driven. More importantly, the mutualism between Remora and underlying system software promises a new direction towards separation of concerns in WSNs. This feature also offers a practical way to develop sensor middleware services which should be generic and developed close to the operating system. Additionally, it allows the customization of sensor software--deploying only application-required system-level services on nodes, instead of installing a fixed large system software image for any application. Our evaluation results show that the deployed Remora applications have an acceptable memory overhead and a negligible CPU cost compared with the state-of-the-art development models.