Electrical measurement is a crucial part of calibration and standard conformity assessment. The main concern in a measurement process is its metrological credibility (i.e. how close/ far is the measurement result to the actual measurand) which is expressed in terms of measurement uncertainty. Measurement uncertainty is of vital importance specially when the measurement results are used by judicial authorities, commercial and fiscal stake beneficiaries, law enforcement personnel or healthcare professionals. For example, when the result of a blood glucose test is relied upon to determine whether a patient needs medication, the measurement uncertainty becomes decisive. For a test expert either involved directly or indirectly in the measurement process or any relevant field, it is of utmost significance to have a hands-on expertise of uncertainty evaluation techniques. This book elaborates the principles of measurement uncertainty evaluation in electrical measurement and explores some important related subjects as well as the most important and frequent applications. In order to explore the uncertainty concepts, the book firstly introduce some basic definitions and discuss concepts from the scientific literature and international standards. Some relevant discussions regarding the components and working principles of measurement systems are also included. The main portion of the book is dedicated to the subject of uncertainty evaluation which is stated via several examples. Uncertainty evaluation is accomplished by identification of a cause-and-effect diagram and formation of an uncertainty budget.