In order to validate user input, ASP.NET provides validation server controls. All validation controls inherits from BaseValidator class which contains the common validation properties and methods like ControlToValidate, Enabled, IsValid, EnableClientScript, ValidationGroup,Validate() etc.
ASP.NET provides a range of validation controls:
RequiredFieldValidator validates compulsory/required input.RangeValidator validates the range. Validates that input falls between the given range values.CompareValidator validates or compares the input of a control with another control value or with a fixed value.RegularExpressionValidator validates input value against a defined regular expression pattern.CustomValidator allows to customize the validation logic with respect to our application logic.ValidationSummary displays all errors on page collectively.