[Truncated abstract] This thesis develops a scheduled protocol (time division multiple access, TDMA) called flexible-schedule-based TDMA Protocol (FlexiTP), to address the problem of providing end-to-end guarantees on data delivery, whilst also respecting severe resource constraints of wireless sensor networks. FlexiTP achieves this balance through a distributed, synchronised, and loose slot structure in which sensor nodes can build, modify, or extend their schedules based on their local information. In FlexiTP, it is not necessary to predetermine the number of slots required for a network. FlexiTP's local repair scheme allows nodes to adjust their schedules dynamically and autonomously to recover from node and communication faults. Hence, it maintains a reliable and selforganising multihop network. Most sensor network protocols designed for data gathering applications implicitly assume a periodic rate of data collection from all nodes in the network to the base station. However, nodes may want to report their data more rapidly or slowly depending on the significance and importance of their data to the end-user. The problem is that traditional TDMA-based protocols are not flexible to changes in traffic patterns because of their rigid slot structure schemes. This thesis aims to solve this problem by developing an ondemand TDMA slot transfer method that leverages the flexible-slot structure algorithm of FlexiTP to transfer time slots from one part of the network to another part. ... While these communication patterns are sufficient for monitoring applications, individual sensor nodes may need to send their data to multiple destination nodes across the network in order to execute a distributed cooperative-function based on their local environment. This peer-to-peer communication pattern makes sensor networks more reactive to triggers from the environment. This thesis attempts to solve the problem of lack of peer-to-peer communication in the design of a TDMA-driven protocol by extending the idea of on-demand TDMA slot transfer method to allow each sensor node in the network to claim extra time slots to communicate with any other nodes (peers) in the network, without going through the base station. Nodes in the network may have different priorities of data because of event-triggering sensor readings or various types of sensor readings (e.g., light, temperature, and humidity) they provide. When nodes with high priority packets increase the frequency of their data collections, the network bandwidth may be dominated by these nodes. It is desirable to allow nodes with low priority packets to aggregate their packets and so enabling these nodes to send their data to the base station under the current available network bandwidth. This thesis proposes an on-demand data aggregation algorithm that enables sensor nodes to perform an in-network-aggregation based on their current sensing requirements and network capacity constraints. In summary, this thesis describes the design, implementation, and evaluation of protocols for wireless sensor networks that focus on achieving energy-efficiency, provisioning performance assurances, and supporting reactivity and adaptability in constantly changing environment.