Probability in Physics : an Introductory Guide This textbook presents an introduction to the use of probability in physics treating introductory ideas of both statistical physics and of statistical inference as well the importance of probability in information theory quantum mechanics and stochastic processes in a unified manner. The book also presents a harmonised view of frequentist and Bayesian approaches to inference emphasising their complementary value. The aim is to steer a middle course between the cookbook style and an overly dry mathematical statistics style. The treatment is driven by real physics examples throughout but developed with a level of mathematical clarity and rigour appropriate to mid career physics undergraduates. Exercises and solutions are included Part I: The Basics Randomness and Probability Distributions Moments and Errors Part II: Frequency Distributions in the Physical World Counting the Ways: Arrangements and Subsets Counting Statistics: Binomial and Poisson Distributions Combining Many Factors: The Gaussian Distribution Distributions Arising from Random Processes in Time Part III: Probabilistic Inference: Reasoning in the Presence of Uncertainty Hypothesis Testing Parameter Estimation Inference With Two Variables: Correlation Testing and Line Fitting Model Fitting Part IV: Selected Topics Information Uncertainty and Surprise Erratic Time Series Probability in Quantum Physics Entropy Complexity and the Arrow of Time Solutions