diff --git a/claims.go b/claims.go
index 4ea64a7..9dee607 100644
--- a/claims.go
+++ b/claims.go
@@ -11,5 +11,6 @@ type Claims interface {
 	GetIssuedAt() (*NumericDate, error)
 	GetNotBefore() (*NumericDate, error)
 	GetIssuer() (string, error)
+	GetSubject() (string, error)
 	GetAudience() (ClaimStrings, error)
 }
diff --git a/errors.go b/errors.go
index 10ac883..34f32fa 100644
--- a/errors.go
+++ b/errors.go
@@ -18,6 +18,7 @@ var (
 	ErrTokenExpired          = errors.New("token is expired")
 	ErrTokenUsedBeforeIssued = errors.New("token used before issued")
 	ErrTokenInvalidIssuer    = errors.New("token has invalid issuer")
+	ErrTokenInvalidSubject   = errors.New("token has invalid subject")
 	ErrTokenNotValidYet      = errors.New("token is not valid yet")
 	ErrTokenInvalidId        = errors.New("token has invalid id")
 	ErrTokenInvalidClaims    = errors.New("token has invalid claims")
@@ -29,11 +30,12 @@ const (
 	ValidationErrorUnverifiable                        // Token could not be verified because of signing problems
 	ValidationErrorSignatureInvalid                    // Signature validation failed
 
-	// Standard Claim validation errors
+	// Registered Claim validation errors
 	ValidationErrorAudience      // AUD validation failed
 	ValidationErrorExpired       // EXP validation failed
 	ValidationErrorIssuedAt      // IAT validation failed
 	ValidationErrorIssuer        // ISS validation failed
+	ValidationErrorSubject       // SUB validation failed
 	ValidationErrorNotValidYet   // NBF validation failed
 	ValidationErrorId            // JTI validation failed
 	ValidationErrorClaimsInvalid // Generic claims validation error
diff --git a/map_claims.go b/map_claims.go
index 9e1857f..a1e4935 100644
--- a/map_claims.go
+++ b/map_claims.go
@@ -36,6 +36,11 @@ func (m MapClaims) GetIssuer() (string, error) {
 	return m.ParseString("iss")
 }
 
+// GetSubject implements the Claims interface.
+func (m MapClaims) GetSubject() (string, error) {
+	return m.ParseString("sub")
+}
+
 // ParseNumericDate tries to parse a key in the map claims type as a number
 // date. This will succeed, if the underlying type is either a [float64] or a
 // [json.Number]. Otherwise, nil will be returned.
diff --git a/registered_claims.go b/registered_claims.go
index ccdd46a..77951a5 100644
--- a/registered_claims.go
+++ b/registered_claims.go
@@ -56,3 +56,8 @@ func (c RegisteredClaims) GetAudience() (ClaimStrings, error) {
 func (c RegisteredClaims) GetIssuer() (string, error) {
 	return c.Issuer, nil
 }
+
+// GetSubject implements the Claims interface.
+func (c RegisteredClaims) GetSubject() (string, error) {
+	return c.Subject, nil
+}
diff --git a/validator.go b/validator.go
index 3fc37ab..0da51af 100644
--- a/validator.go
+++ b/validator.go
@@ -24,9 +24,17 @@ type Validator struct {
 	// unrealistic, i.e., in the future.
 	verifyIat bool
 
-	// expectedAud contains the audiences this token expects. Supplying an empty
+	// expectedAud contains the audience this token expects. Supplying an empty
 	// string will disable aud checking.
 	expectedAud string
+
+	// expectedIss contains the issuer this token expects. Supplying an empty
+	// string will disable iss checking.
+	expectedIss string
+
+	// expectedSub contains the subject this token expects. Supplying an empty
+	// string will disable sub checking.
+	expectedSub string
 }
 
 // CustomClaims represents a custom claims interface, which can be built upon the integrated
@@ -60,28 +68,42 @@ func (v *Validator) Validate(claims Claims) error {
 		now = time.Now()
 	}
 
+	// We always need to check the expiration time, but the claim itself is OPTIONAL
 	if !v.VerifyExpiresAt(claims, now, false) {
 		vErr.Inner = ErrTokenExpired
 		vErr.Errors |= ValidationErrorExpired
 	}
 
-	// Check iat if the option is enabled
-	if v.verifyIat && !v.VerifyIssuedAt(claims, now, false) {
-		vErr.Inner = ErrTokenUsedBeforeIssued
-		vErr.Errors |= ValidationErrorIssuedAt
-	}
-
+	// We always need to check not-before, but the claim itself is OPTIONAL
 	if !v.VerifyNotBefore(claims, now, false) {
 		vErr.Inner = ErrTokenNotValidYet
 		vErr.Errors |= ValidationErrorNotValidYet
 	}
 
+	// Check issued-at if the option is enabled
+	if v.verifyIat && !v.VerifyIssuedAt(claims, now, false) {
+		vErr.Inner = ErrTokenUsedBeforeIssued
+		vErr.Errors |= ValidationErrorIssuedAt
+	}
+
 	// If we have an expected audience, we also require the audience claim
 	if v.expectedAud != "" && !v.VerifyAudience(claims, v.expectedAud, true) {
 		vErr.Inner = ErrTokenInvalidAudience
 		vErr.Errors |= ValidationErrorAudience
 	}
 
+	// If we have an expected issuer, we also require the issuer claim
+	if v.expectedIss != "" && !v.VerifyIssuer(claims, v.expectedIss, true) {
+		vErr.Inner = ErrTokenInvalidIssuer
+		vErr.Errors |= ValidationErrorIssuer
+	}
+
+	// If we have an expected subject, we also require the subject claim
+	if v.expectedSub != "" && !v.VerifySubject(claims, v.expectedSub, true) {
+		vErr.Inner = ErrTokenInvalidSubject
+		vErr.Errors |= ValidationErrorSubject
+	}
+
 	// Finally, we want to give the claim itself some possibility to do some
 	// additional custom validation based on their custom claims
 	cvt, ok := claims.(CustomClaims)
@@ -166,6 +188,17 @@ func (v *Validator) VerifyIssuer(claims Claims, cmp string, req bool) bool {
 	return verifyIss(iss, cmp, req)
 }
 
+// VerifySubject compares the sub claim against cmp.
+// If required is false, this method will return true if the value matches or is unset
+func (v *Validator) VerifySubject(claims Claims, cmp string, req bool) bool {
+	iss, err := claims.GetSubject()
+	if err != nil {
+		return false
+	}
+
+	return verifySub(iss, cmp, req)
+}
+
 // ----- helpers
 
 func verifyAud(aud []string, cmp string, required bool) bool {
@@ -221,9 +254,14 @@ func verifyIss(iss string, cmp string, required bool) bool {
 	if iss == "" {
 		return !required
 	}
-	if subtle.ConstantTimeCompare([]byte(iss), []byte(cmp)) != 0 {
-		return true
-	} else {
-		return false
-	}
+
+	return iss == cmp
+}
+
+func verifySub(sub string, cmp string, required bool) bool {
+	if sub == "" {
+		return !required
+	}
+
+	return sub == cmp
 }
diff --git a/validator_option.go b/validator_option.go
index 8c7d30b..4a75fea 100644
--- a/validator_option.go
+++ b/validator_option.go
@@ -33,9 +33,41 @@ func WithIssuedAt() ValidatorOption {
 	}
 }
 
-// WithAudience returns the ValidatorOption to set the expected audience.
+// WithAudience configures the validator to require the specified audience in
+// the `aud` claim. Validation will fail if the audience is not listed in the
+// token or the `aud` claim is missing.
+//
+// NOTE: While the `aud` claim is OPTIONAL is a JWT, the handling of it is
+// application-specific. Since this validation API is helping developers in
+// writing secure application, we decided to REQUIRE the existence of the claim.
 func WithAudience(aud string) ValidatorOption {
 	return func(v *Validator) {
 		v.expectedAud = aud
 	}
 }
+
+// WithIssuer configures the validator to require the specified issuer in the
+// `iss` claim. Validation will fail if a different issuer is specified in the
+// token or the `iss` claim is missing.
+//
+// NOTE: While the `iss` claim is OPTIONAL is a JWT, the handling of it is
+// application-specific. Since this validation API is helping developers in
+// writing secure application, we decided to REQUIRE the existence of the claim.
+func WithIssuer(iss string) ValidatorOption {
+	return func(v *Validator) {
+		v.expectedIss = iss
+	}
+}
+
+// WithSubject configures the validator to require the specified subject in the
+// `sub` claim. Validation will fail if a different subject is specified in the
+// token or the `sub` claim is missing.
+//
+// NOTE: While the `sub` claim is OPTIONAL is a JWT, the handling of it is
+// application-specific. Since this validation API is helping developers in
+// writing secure application, we decided to REQUIRE the existence of the claim.
+func WithSubject(sub string) ValidatorOption {
+	return func(v *Validator) {
+		v.expectedSub = sub
+	}
+}