diff --git a/httpie/cli/argparser.py b/httpie/cli/argparser.py
index 2b9ac936..ffe2dd24 100644
--- a/httpie/cli/argparser.py
+++ b/httpie/cli/argparser.py
@@ -284,8 +284,7 @@ class HTTPieArgumentParser(argparse.ArgumentParser):
                 invalid.append(option)
 
         if invalid:
-            msg = 'unrecognized arguments: %s'
-            self.error(msg % ' '.join(invalid))
+            self.error(f'unrecognized arguments: {" ".join(invalid)}')
 
     def _body_from_file(self, fd):
         """Read the data from a file-like object.
@@ -381,8 +380,8 @@ class HTTPieArgumentParser(argparse.ArgumentParser):
             for key, file in self.args.files.items():
                 if key != '':
                     self.error(
-                        'Invalid file fields (perhaps you meant --form?): %s'
-                        % ','.join(self.args.files.keys()))
+                        'Invalid file fields (perhaps you meant --form?):'
+                        f' {",".join(self.args.files.keys())}')
                 if request_file is not None:
                     self.error("Can't read request from multiple files")
                 request_file = file
@@ -407,10 +406,7 @@ class HTTPieArgumentParser(argparse.ArgumentParser):
         def check_options(value, option):
             unknown = set(value) - OUTPUT_OPTIONS
             if unknown:
-                self.error('Unknown output options: {0}={1}'.format(
-                    option,
-                    ','.join(unknown)
-                ))
+                self.error(f'Unknown output options: {option}={",".join(unknown)}')
 
         if self.args.verbose:
             self.args.all = True
diff --git a/httpie/cli/definition.py b/httpie/cli/definition.py
index cd376328..5926968e 100644
--- a/httpie/cli/definition.py
+++ b/httpie/cli/definition.py
@@ -30,7 +30,7 @@ from ..ssl import AVAILABLE_SSL_VERSION_ARG_MAPPING, DEFAULT_SSL_CIPHERS
 
 parser = HTTPieArgumentParser(
     prog='http',
-    description='%s <https://httpie.org>' % __doc__.strip(),
+    description=f'{__doc__.strip()} <https://httpie.org>',
     epilog=dedent('''
     For every --OPTION there is also a --no-OPTION that reverts OPTION
     to its default value.
@@ -267,7 +267,7 @@ output_processing.add_argument(
     '''.format(
         default=DEFAULT_STYLE,
         available_styles='\n'.join(
-            '{0}{1}'.format(8 * ' ', line.strip())
+            f'        {line.strip()}'
             for line in wrap(', '.join(sorted(AVAILABLE_STYLES)), 60)
         ).strip(),
         auto_style=AUTO_STYLE,
@@ -330,7 +330,7 @@ output_processing.add_argument(
 
     '''.format(
         option_list='\n'.join(
-            (8 * ' ') + option for option in DEFAULT_FORMAT_OPTIONS).strip()
+            f'        {option}' for option in DEFAULT_FORMAT_OPTIONS).strip()
     )
 )
 
@@ -383,12 +383,12 @@ output_options.add_argument(
     '--verbose', '-v',
     dest='verbose',
     action='store_true',
-    help='''
+    help=f'''
     Verbose output. Print the whole request as well as the response. Also print
     any intermediary requests/responses (such as redirects).
-    It's a shortcut for: --all --print={0}
+    It's a shortcut for: --all --print={''.join(OUTPUT_OPTIONS)}
 
-    '''.format(''.join(OUTPUT_OPTIONS))
+    '''
 )
 output_options.add_argument(
     '--all',
@@ -562,7 +562,7 @@ auth.add_argument(
             name=plugin.name,
             package=(
                 '' if issubclass(plugin, BuiltinAuthPlugin)
-                else ' (provided by %s)' % plugin.package_name
+                else f' (provided by {plugin.package_name})'
             ),
             description=(
                 '' if not plugin.description else
diff --git a/httpie/cli/requestitems.py b/httpie/cli/requestitems.py
index 977faaeb..3ddc6f62 100644
--- a/httpie/cli/requestitems.py
+++ b/httpie/cli/requestitems.py
@@ -89,13 +89,11 @@ def process_header_arg(arg: KeyValueArg) -> Optional[str]:
 
 
 def process_empty_header_arg(arg: KeyValueArg) -> str:
-    if arg.value:
-        raise ParseError(
-            'Invalid item "%s" '
-            '(to specify an empty header use `Header;`)'
-            % arg.orig
-        )
-    return arg.value
+    if not arg.value:
+        return arg.value
+    raise ParseError(
+        f'Invalid item {arg.orig!r} (to specify an empty header use `Header;`)'
+    )
 
 
 def process_query_param_arg(arg: KeyValueArg) -> str:
@@ -109,7 +107,7 @@ def process_file_upload_arg(arg: KeyValueArg) -> Tuple[str, IO, str]:
     try:
         f = open(os.path.expanduser(filename), 'rb')
     except IOError as e:
-        raise ParseError('"%s": %s' % (arg.orig, e))
+        raise ParseError(f'{arg.orig!r}: {e}')
     return (
         os.path.basename(filename),
         f,
@@ -142,12 +140,11 @@ def load_text_file(item: KeyValueArg) -> str:
         with open(os.path.expanduser(path), 'rb') as f:
             return f.read().decode()
     except IOError as e:
-        raise ParseError('"%s": %s' % (item.orig, e))
+        raise ParseError(f'{item.orig!r}: {e}')
     except UnicodeDecodeError:
         raise ParseError(
-            '"%s": cannot embed the content of "%s",'
+            f'{item.orig!r}: cannot embed the content of {item.value!r},'
             ' not a UTF8 or ASCII-encoded text file'
-            % (item.orig, item.value)
         )
 
 
@@ -155,4 +152,4 @@ def load_json(arg: KeyValueArg, contents: str) -> JSONType:
     try:
         return load_json_preserve_order(contents)
     except ValueError as e:
-        raise ParseError('"%s": %s' % (arg.orig, e))
+        raise ParseError(f'{arg.orig!r}: {e}')
diff --git a/httpie/core.py b/httpie/core.py
index 2767e300..1cb1c8b4 100644
--- a/httpie/core.py
+++ b/httpie/core.py
@@ -205,10 +205,9 @@ def program(args: argparse.Namespace, env: Environment) -> ExitStatus:
             if downloader.interrupted:
                 exit_status = ExitStatus.ERROR
                 env.log_error(
-                    'Incomplete download: size=%d; downloaded=%d' % (
-                        downloader.status.total_size,
-                        downloader.status.downloaded
-                    ))
+                    f'Incomplete download: size={downloader.status.total_size};'
+                    f' downloaded={downloader.status.downloaded}'
+                )
         return exit_status
 
     finally:
diff --git a/httpie/downloads.py b/httpie/downloads.py
index 8ac61388..22e2d4a9 100644
--- a/httpie/downloads.py
+++ b/httpie/downloads.py
@@ -64,7 +64,7 @@ def parse_content_range(content_range: str, resumed_from: int) -> int:
 
     if not match:
         raise ContentRangeError(
-            'Invalid Content-Range format %r' % content_range)
+            f'Invalid Content-Range format {content_range!r}')
 
     content_range_dict = match.groupdict()
     first_byte_pos = int(content_range_dict['first_byte_pos'])
@@ -85,16 +85,15 @@ def parse_content_range(content_range: str, resumed_from: int) -> int:
         or (instance_length is not None
             and instance_length <= last_byte_pos)):
         raise ContentRangeError(
-            'Invalid Content-Range returned: %r' % content_range)
+            f'Invalid Content-Range returned: {content_range!r}')
 
     if (first_byte_pos != resumed_from
         or (instance_length is not None
             and last_byte_pos + 1 != instance_length)):
         # Not what we asked for.
         raise ContentRangeError(
-            'Unexpected Content-Range returned (%r)'
-            ' for the requested Range ("bytes=%d-")'
-            % (content_range, resumed_from)
+            f'Unexpected Content-Range returned ({content_range!r})'
+            f' for the requested Range ("bytes={resumed_from}-")'
         )
 
     return last_byte_pos + 1
@@ -112,7 +111,7 @@ def filename_from_content_disposition(
     """
     # attachment; filename=jakubroztocil-httpie-0.4.1-20-g40bd8f6.tar.gz
 
-    msg = Message('Content-Disposition: %s' % content_disposition)
+    msg = Message(f'Content-Disposition: {content_disposition}')
     filename = msg.get_filename()
     if filename:
         # Basic sanitation.
@@ -177,7 +176,7 @@ def trim_filename_if_needed(filename: str, directory='.', extra=0) -> str:
 def get_unique_filename(filename: str, exists=os.path.exists) -> str:
     attempt = 0
     while True:
-        suffix = '-' + str(attempt) if attempt > 0 else ''
+        suffix = f'-{attempt}' if attempt > 0 else ''
         try_filename = trim_filename_if_needed(filename, extra=len(suffix))
         try_filename += suffix
         if not exists(try_filename):
@@ -226,7 +225,7 @@ class Downloader:
             if bytes_have:
                 # Set ``Range`` header to resume the download
                 # TODO: Use "If-Range: mtime" to make sure it's fresh?
-                request_headers['Range'] = 'bytes=%d-' % bytes_have
+                request_headers['Range'] = f'bytes={bytes_have}-'
                 self._resumed_from = bytes_have
 
     def start(
@@ -288,12 +287,8 @@ class Downloader:
         )
 
         self._progress_reporter.output.write(
-            'Downloading %sto "%s"\n' % (
-                (humanize_bytes(total_size) + ' '
-                 if total_size is not None
-                 else ''),
-                self._output_file.name
-            )
+            f'Downloading {humanize_bytes(total_size) + " " if total_size is not None else ""}'
+            f'to "{self._output_file.name}"\n'
         )
         self._progress_reporter.start()
 
@@ -442,7 +437,7 @@ class ProgressReporterThread(threading.Thread):
                     s = int((self.status.total_size - downloaded) / speed)
                     h, s = divmod(s, 60 * 60)
                     m, s = divmod(s, 60)
-                    eta = '{0}:{1:0>2}:{2:0>2}'.format(h, m, s)
+                    eta = f'{h}:{m:0>2}:{s:0>2}'
 
                 self._status_line = PROGRESS.format(
                     percentage=percentage,
@@ -455,11 +450,7 @@ class ProgressReporterThread(threading.Thread):
             self._prev_bytes = downloaded
 
         self.output.write(
-            CLEAR_LINE
-            + ' '
-            + SPINNER[self._spinner_pos]
-            + ' '
-            + self._status_line
+            f'{CLEAR_LINE} {SPINNER[self._spinner_pos]} {self._status_line}'
         )
         self.output.flush()
 
diff --git a/httpie/models.py b/httpie/models.py
index ab45ed6c..d496f81a 100644
--- a/httpie/models.py
+++ b/httpie/models.py
@@ -102,7 +102,7 @@ class HTTPRequest(HTTPMessage):
         request_line = '{method} {path}{query} HTTP/1.1'.format(
             method=self._orig.method,
             path=url.path or '/',
-            query='?' + url.query if url.query else ''
+            query=f'?{url.query}' if url.query else ''
         )
 
         headers = dict(self._orig.headers)
@@ -110,10 +110,7 @@ class HTTPRequest(HTTPMessage):
             headers['Host'] = url.netloc.split('@')[-1]
 
         headers = [
-            '%s: %s' % (
-                name,
-                value if isinstance(value, str) else value.decode('utf8')
-            )
+            f'{name}: {value if isinstance(value, str) else value.decode("utf-8")}'
             for name, value in headers.items()
         ]
 
diff --git a/httpie/output/formatters/colors.py b/httpie/output/formatters/colors.py
index 2d72e63b..384eefdf 100644
--- a/httpie/output/formatters/colors.py
+++ b/httpie/output/formatters/colors.py
@@ -120,8 +120,8 @@ def get_lexer(
         subtype_name, subtype_suffix = subtype.split('+', 1)
         lexer_names.extend([subtype_name, subtype_suffix])
         mime_types.extend([
-            '%s/%s' % (type_, subtype_name),
-            '%s/%s' % (type_, subtype_suffix)
+            f'{type_}/{subtype_name}',
+            f'{type_}/{subtype_suffix}',
         ])
 
     # As a last resort, if no lexer feels responsible, and
diff --git a/httpie/plugins/builtin.py b/httpie/plugins/builtin.py
index 0a4630a7..085d4d29 100644
--- a/httpie/plugins/builtin.py
+++ b/httpie/plugins/builtin.py
@@ -29,9 +29,9 @@ class HTTPBasicAuth(requests.auth.HTTPBasicAuth):
 
     @staticmethod
     def make_header(username: str, password: str) -> str:
-        credentials = u'%s:%s' % (username, password)
-        token = b64encode(credentials.encode('utf8')).strip().decode('latin1')
-        return 'Basic %s' % token
+        credentials = f'{username}:{password}'
+        token = b64encode(credentials.encode('utf-8')).strip().decode('latin1')
+        return f'Basic {token}'
 
 
 class BasicAuthPlugin(BuiltinAuthPlugin):
diff --git a/httpie/utils.py b/httpie/utils.py
index fddf15ad..e7ebf68a 100644
--- a/httpie/utils.py
+++ b/httpie/utils.py
@@ -62,7 +62,7 @@ def humanize_bytes(n, precision=2):
             break
 
     # noinspection PyUnboundLocalVariable
-    return '%.*f %s' % (precision, n / factor, suffix)
+    return f'{n / factor:.{precision}f} {suffix}'
 
 
 class ExplicitNullAuth(requests.auth.AuthBase):
@@ -85,7 +85,7 @@ def get_content_type(filename):
     if mime:
         content_type = mime
         if encoding:
-            content_type = '%s; charset=%s' % (mime, encoding)
+            content_type = f'{mime}; charset={encoding}'
         return content_type