Bayes’ Theorem is a fundamental principle in probability theory and statistics that describes how to update the probability of a hypothesis or event based on new evidence. It is named after Thomas Bayes, an 18th-century mathematician.

The theorem can be stated as follows:

**P(A|B) = (P(B|A) * P(A)) / P(B)
**

Where:

- P(A|B) is the conditional probability of event A given event B.
- P(B|A) is the conditional probability of event B given event A.
- P(A) is the probability of event A.
- P(B) is the probability of event B.

Bayes’ Theorem allows us to calculate the updated probability of a hypothesis (event A) given new evidence (event B) by combining our prior knowledge (prior probability) and the likelihood of observing the evidence.

The steps to apply Bayes’ Theorem are as follows:

- Determine the prior probability: Assess the initial probability of the hypothesis (event A) based on prior knowledge or assumptions.
- Gather new evidence: Obtain new evidence (event B) that is relevant to the hypothesis.
- Determine the likelihood: Determine the conditional probability of observing the evidence (event B) given the hypothesis (event A).
- Calculate the posterior probability: Use Bayes’ Theorem to calculate the updated probability of the hypothesis (event A) given the new evidence (event B).

Bayes’ Theorem is widely used in various fields, including statistics, machine learning, and artificial intelligence. It is particularly valuable in situations where new evidence needs to be incorporated to update beliefs or make predictions based on prior knowledge.

Note that Bayes’ Theorem assumes that the events are independent and that the prior probabilities and conditional probabilities are known or can be estimated accurately.