Undergraduate students of physics and engineering need to develop an understanding of the nature of random experimental errors and of how to present experimental results, taking proper account of these errors. This book is designed as a laboratory workbook, introducing simple ideas within the reader's experience and building upon them in order to enable students to present results in a clear and accurate manner, before mastering the underlying theory. Confidence in using statistical methods in practical situations is established by this 'common sense' approach, encouraging the student to progress to more complex theoretical concepts. All the mathematical techniques required are developed in the book so reference to other texts is not necessary. Problems and examples are provided at the ends of sections, in order not to disturb the flow of the narrative, and a summary of the main results needed for practical purposes is given at the end of the book.