This book comprehensively covers the requirements of Tanzanian syllabus for Science for Standard Three 2023 using the Competence-based approach. It has plenty of activities, experiments and exercises that will engage the pupil and raise his/her interest in Science. The language used is simple and straightforward and concepts are introduced from using a very practical approach. Where applicable, we have introduced or demonstrated concepts using simple experiments and activities. This approach intends to develop inquisitiveness and investigative skills in the pupil from an early age. At the end of each section, there are exercises which test the pupil’s understanding of concepts covered. Through over 40 exercises, we hope to help young learners to practise and develop their Scientific skills. We believe that this book will provide a strong foundation for the Science, inculcate interest in Science and give the pupil fundamental knowledge and skills essential for higher classes.