Pessimistic Concurrency Control is a database management technique that assumes conflicts will occur when multiple transactions access the same data. To prevent these conflicts, it locks the data before any transaction can read or modify it. This ensures that only one transaction can access the data at a time, reducing the risk of inconsistencies. However, this approach can lead to decreased performance, especially in systems with high transaction volumes. If one transaction holds a lock, others must wait, which can create bottlenecks. Despite this, Pessimistic Concurrency Control is useful in scenarios where data integrity is critical.