diff --git a/amanuensis/cli/lexicon.py b/amanuensis/cli/lexicon.py
index d4bdcde..41a8018 100644
--- a/amanuensis/cli/lexicon.py
+++ b/amanuensis/cli/lexicon.py
@@ -122,7 +122,25 @@ def command_player_add(args):
 	"""
 	Add a player to a lexicon
 	"""
-	raise NotImplementedError() # TODO
+	# Module imports
+	from config import logger
+	from lexicon import LexiconModel
+	from lexicon.manage import add_player
+	from user import UserModel
+
+	# Verify arguments
+	u = UserModel.by(name=args.username)
+	if u is None:
+		logger.error("Could not find user '{}'".format(args.username))
+		return -1
+	lex = LexiconModel.by(name=args.lexicon)
+	if lex is None:
+		logger.error("Could not find lexicon '{}'".format(args.lexicon))
+		return -1
+
+	# Internal call
+	add_player(lex, u)
+
 
 @requires_lexicon
 @requires_username
@@ -133,7 +151,28 @@ def command_player_remove(args):
 	Removing a player dissociates them from any characters
 	they control but does not delete any character data.
 	"""
-	raise NotImplementedError() # TODO
+	# Module imports
+	from config import logger
+	from lexicon import LexiconModel
+	from lexicon.manage import remove_player
+	from user import UserModel
+
+	# Verify arguments
+	u = UserModel.by(name=args.username)
+	if u is None:
+		logger.error("Could not find user '{}'".format(args.username))
+		return -1
+	lex = LexiconModel.by(name=args.lexicon)
+	if lex is None:
+		logger.error("Could not find lexicon '{}'".format(args.lexicon))
+		return -1
+	if lex.editor == u.id:
+		logger.error("Can't remove the editor of a lexicon")
+		return -1
+
+	# Internal call
+	remove_player(lex, u)
+
 
 @requires_lexicon
 def command_player_list(args):
diff --git a/amanuensis/lexicon/manage.py b/amanuensis/lexicon/manage.py
index 02c5c5b..7fe0763 100644
--- a/amanuensis/lexicon/manage.py
+++ b/amanuensis/lexicon/manage.py
@@ -94,4 +94,71 @@ def get_all_lexicons():
 	# Load all of the lexicons
 	lexes = map(lambda id: lexicon.LexiconModel.by(lid=id), lids)
 
-	return lexes
\ No newline at end of file
+	return lexes
+
+
+def valid_add(lex, player, password=None):
+	"""
+	Checks whether the given player can join a lexicon
+	"""
+	# Trivial failures
+	if lex is None:
+		return False
+	if player is None:
+		return False
+	# Can't join if already in the game
+	if player.id in lex.join.joined:
+		return False
+	# Can't join if the game is closed
+	if not lex.join.open:
+		return False
+	# Can't join if the player max is reached
+	if len(lex.join.joined) >= lex.join.max_players:
+		return False
+	# Can't join if the password doesn't check out
+	if lex.join.password is not None and lex.join.password != password:
+		return False
+
+	return True
+
+
+def add_player(lex, player):
+	"""
+	Unconditionally adds a player to a lexicon
+	"""
+	# Verify arguments
+	if lex is None:
+		raise ValueError("Invalid lexicon: '{}'".format(lex))
+	if player is None:
+		raise ValueError("Invalid player: '{}'".format(player))
+
+	# Idempotently add player
+	with config.json_rw(lex.config_path) as cfg:
+		if player.id not in cfg.join.joined:
+			cfg.join.joined.append(player.id)
+
+
+def remove_player(lex, player):
+	"""
+	Remove a player from a lexicon
+	"""
+	# Verify arguments
+	if lex is None:
+		raise ValueError("Invalid lexicon: '{}'".format(lex))
+	if player is None:
+		raise ValueError("Invalid player: '{}'".format(player))
+	if lex.editor == player.id:
+		raise ValueError("Can't remove the editor '{}' from lexicon '{}'".format(player.username, lex.name))
+
+	# Idempotently remove player
+	with config.json_rw(lex.config_path) as cfg:
+		if player.id in cfg.join.joined:
+			cfg.join.joined.remove(player.id)
+
+	# TODO Reassign the player's characters to the editor
+
+
+def list_players(lex):
+	"""
+	"""
+	pass
\ No newline at end of file