diff --git a/libpurple_to_markdown/__init__.py b/libpurple_to_markdown/__init__.py
index f150ae8..078c2fd 100644
--- a/libpurple_to_markdown/__init__.py
+++ b/libpurple_to_markdown/__init__.py
@@ -26,18 +26,42 @@ Matrix.
 
 ## Usage
 
-From the repository root:
+There are two main import patterns:
+
+- One-off archival import: For when you have a large set of messages to import
+  for a service that you don't use very much anymore.
+- Recurring import: For when you are still using the service, and want to
+  import on a recurring basis.
+
+This program will be default not overwrite existing files, as the user might
+have modified it.
+
+Special consideration must be taking for recurring imports if you expect to be
+modifying the resulting files, for example if you are inserting links
+using Obsidian's unlinked mentions feature. You might want to use the
+`--skip-this-period` flag to avoid importing the current period until it has
+become the last period. That way you won't accidentally modify the log, because
+it has been finalized.
+
+### One-off
+
+This is the recommended command for the one-off case:
 
 ```bash
 python -m libpurple_to_markdown LOG_DIRECTORY --output OUTPUT_FOLDER
 ```
 
-It was made specifically for import into Obsidian, so it might not suite your
-purposes, but it shouldn't be too difficult to adjust the formatting code.
+### Recurring
+
+This is the recommended command for the recurring import case:
+
+```bash
+python -m libpurple_to_markdown LOG_DIRECTORY --output OUTPUT_FOLDER --skip-this-period --period month
+```
 
 ## TODO
 
-- [ ] Decode MMS parts and reconstruct image attachments.
+- [ ] SyncTech: Decode MMS parts and reconstruct image attachments.
 """
 
 import dataclasses
diff --git a/libpurple_to_markdown/__main__.py b/libpurple_to_markdown/__main__.py
index 12570a0..ba8f893 100644
--- a/libpurple_to_markdown/__main__.py
+++ b/libpurple_to_markdown/__main__.py
@@ -43,24 +43,27 @@ def year_quarter_period_key(msg: Message):
 
 MAX_AVERAGE_MESSAGES_PER_PERIOD = 120
 
+PERIOD_KEYS_BY_NAME = {
+        'full': (lambda msg: 'full'),
+        'year': year_period_key,
+        'quarter': year_quarter_period_key,
+        'month': year_and_month_period_key,
+}
 
-def group_messages_by_period(messages: Iterable[Message]) -> dict[str, list[Message]]:
-    possible_period_keys = [
-        (lambda msg: 'full'),
-        year_period_key,
-        year_quarter_period_key,
-        year_and_month_period_key,
-    ]
 
-    for period_key in possible_period_keys:
+def group_messages_by_period(messages: Iterable[Message], period_key: str | None = None) -> dict[str, list[Message]]:
+    possible_period_keys = PERIOD_KEYS_BY_NAME.values()
+    if period_key is not None:
+        possible_period_keys  = [PERIOD_KEYS_BY_NAME[period_key]]
+    for period_key_fn in possible_period_keys:
         grouped = group_messages(messages, key=period_key)
         average_num_messages = sum(len(grouped[k]) for k in grouped) / len(grouped)
         if average_num_messages <= MAX_AVERAGE_MESSAGES_PER_PERIOD:
             break
 
-        del period_key, average_num_messages
+        del average_num_messages
 
-    return grouped
+    return grouped, period_key_fn
 
 
 def replace_myself(messages: Iterable[Message], myself: str) -> Iterator[Message]:
@@ -77,9 +80,13 @@ def parse_args():
     parser.add_argument('--synctech', type=Path, dest='synctech_sms_backup_file')
     parser.add_argument('--output', type=Path)
     parser.add_argument('--myself', type=str, default='Myself')
+    parser.add_argument('--overwrite', action='store_true', dest='overwrite_files')
+    parser.add_argument('--period', dest='period_key', values=list(PERIOD_KEYS_BY_NAME.keys()))
+    parser.add_argument('--skip-this-period', action='store_true', dest='skip_this_period')
     return parser.parse_args()
 
 
+
 def main():
     logging.basicConfig()
     logging.getLogger().setLevel('INFO')
@@ -112,7 +119,7 @@ def main():
             logger.info('  "%s": Skipped due to too few messages', chat_id)
             continue
 
-        messages_by_period = group_messages_by_period(messages_in_chat)
+        messages_by_period, period_key_fn = group_messages_by_period(messages_in_chat, args.period_key)
         logger.info(
             '  "%s": %d messages, %d periods (%d msg/period avg)',
             chat_id,
@@ -121,22 +128,34 @@ def main():
             len(messages_in_chat_original) / len(messages_by_period),
         )
 
-        for period_key, messages in messages_by_period.items():
+        this_period_name = period_key_fn(datetime.datetime.now())
+
+        for period_key_name, messages in messages_by_period.items():
             file_escaped_chat_id = chat_id.replace(' ', '-')
             output_file = (
-                args.output / chat_id / f'{file_escaped_chat_id}-{period_key}.md'
+                args.output / chat_id / f'{file_escaped_chat_id}-{period_key_name}.md'
             )
-            output_file.parent.mkdir(exist_ok=True)
+
             logger.info('Writing % 5d messages to %s', len(messages), output_file)
+
+            if this_period_name == period_key_name:
+                logger.info('Skipping due to --skip-this-period: %s', output_file)
+                continue
+            if output_file.exists() and not args.overwrite_files:
+                logger.info('Skipping existing file: %s', output_file)
+                continue
+
+            # Create folders and file
+            output_file.parent.mkdir(exist_ok=True)
             with open(output_file, 'w') as f:
                 f.write(
                     format_messages(
                         messages,
-                        title=f'{chat_id} - {period_key}',
+                        title=f'{chat_id} - {period_key_name}',
                     ),
                 )
 
-            del period_key, messages, output_file
+            del period_key_name, messages, output_file
         del chat_id, messages_in_chat_original, messages_in_chat