diff --git a/src/validators/email.py b/src/validators/email.py
index f1fb3f6f..5b57395c 100644
--- a/src/validators/email.py
+++ b/src/validators/email.py
@@ -85,7 +85,7 @@ def email(
         )
         if re.match(
             # dot-atom
-            r"(^[-!#$%&'*+/=?^_`{}|~0-9A-Z]+(\.[-!#$%&'*+/=?^_`{}|~0-9A-Z]+)*$"
+            r"(^[-!#$%&'*+/=?^_`{}|~0-9a-z]+(\.[-!#$%&'*+/=?^_`{}|~0-9a-z]+)*$"
             # quoted-string
             + r'|^"([\001-\010\013\014\016-\037!#-\[\]-\177]|\\[\001-\011\013\014\016-\177])*"$)',
             username_part,
diff --git a/src/validators/hostname.py b/src/validators/hostname.py
index dd7e6991..55b30647 100644
--- a/src/validators/hostname.py
+++ b/src/validators/hostname.py
@@ -25,7 +25,7 @@ def _simple_hostname_regex():
     """Simple hostname validation regex."""
     # {0,59} because two characters are already matched at
     # the beginning and at the end, making the range {1, 61}
-    return re.compile(r"^(?!-)[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,59}[a-zA-Z0-9])?(?<!-)$")
+    return re.compile(r"^(?!-)[a-z0-9](?:[a-z0-9-]{0,59}[a-z0-9])?(?<!-)$", re.IGNORECASE)
 
 
 def _port_validator(value: str):
diff --git a/src/validators/iban.py b/src/validators/iban.py
index 01925972..2b1a4d4d 100644
--- a/src/validators/iban.py
+++ b/src/validators/iban.py
@@ -38,7 +38,7 @@ def iban(value: str, /):
         (ValidationError): If `value` is an invalid IBAN code.
     """
     return (
-        (re.match(r"^[A-Z]{2}[0-9]{2}[A-Z0-9]{11,30}$", value) and _mod_check(value))
+        (re.match(r"^[a-z]{2}[0-9]{2}[a-z0-9]{11,30}$", value, re.IGNORECASE) and _mod_check(value))
         if value
         else False
     )
diff --git a/src/validators/url.py b/src/validators/url.py
index 177e94d1..3c86f0a6 100644
--- a/src/validators/url.py
+++ b/src/validators/url.py
@@ -14,7 +14,7 @@
 def _username_regex():
     return re.compile(
         # dot-atom
-        r"(^[-!#$%&'*+/=?^_`{}|~0-9A-Z]+(\.[-!#$%&'*+/=?^_`{}|~0-9A-Z]+)*$"
+        r"(^[-!#$%&'*+/=?^_`{}|~0-9a-z]+(\.[-!#$%&'*+/=?^_`{}|~0-9a-z]+)*$"
         # non-quoted-string
         + r"|^([\001-\010\013\014\016-\037!#-\[\]-\177]|\\[\001-\011\013\014\016-\177])*$)",
         re.IGNORECASE,
@@ -25,7 +25,7 @@ def _username_regex():
 def _path_regex():
     return re.compile(
         # allowed symbols
-        r"^[\/a-zA-Z0-9\-\.\_\~\!\$\&\'\(\)\*\+\,\;\=\:\@\%"
+        r"^[\/a-z0-9\-\.\_\~\!\$\&\'\(\)\*\+\,\;\=\:\@\%"
         # emoticons / emoji
         + r"\U0001F600-\U0001F64F"
         # multilingual unicode ranges
@@ -133,7 +133,9 @@ def _validate_optionals(path: str, query: str, fragment: str, strict_query: bool
             optional_segments &= True
     if fragment:
         # See RFC3986 Section 3.5 Fragment for allowed characters
-        optional_segments &= bool(re.fullmatch(r"[0-9a-zA-Z?/:@\-._~%!$&'()*+,;=]*", fragment))
+        optional_segments &= bool(
+            re.fullmatch(r"[0-9a-z?/:@\-._~%!$&'()*+,;=]*", fragment, re.IGNORECASE)
+        )
     return optional_segments