diff --git a/README.md b/README.md
index 151c3f4..87b6689 100644
--- a/README.md
+++ b/README.md
@@ -26,12 +26,22 @@ This function is used to tell the library what command line arguments you accept
     cmdarg 'u:' 'source_ldap_username' 'Source (old) LDAP Username'
     cmdarg 'c:' 'groupmap' 'A CSV file mapping usernames to groups that they should belong to post-conversion' '' 'test -e $OPTARG'
 
-All arguments are OPTIONAL by default. An argument that has ':' on the end of its single character option, and does not specify a default value (empty string is considered "not specified"), is REQUIRED. The arguments can be set on the command line either via '-X' or '--Y', where X is the short option and Y is the long option. Example:
+The first argument to cmdarg must be an argument specification. Argument specifications take the form 'NOT', where:
+
+- N : The single letter Name of the argument
+- O : Whether the option is optional or not. Use ':' here for a required argument, '?' for an optional argument. If you provide a default value for a required argument (:), then it becomes optional.
+- T : The type. Leave empty for a string argument, use '[]' for an array argument, use '{}' for a hash argument.
+
+If O and T are both unset, and only the single letter N is provided, then the argument is a boolean argument which will default to false.
+
+The arguments can be set on the command line either via '-X' or '--Y', where X is the short option and Y is the long option. Example:
 
     cmdarg 'r:' 'required-thing' 'Some thing I require'
+    cmdarg 'o?' 'optional-thing' 'Some optional thing'
+    cmdarg 'b' 'boolean-thing' 'Some boolean thing'
 
-    # your_script.sh -r some_thingy
-    # your_script.sh --required-thing some_thingy
+    # your_script.sh -r some_thingy -b -o optional_thing
+    # your_script.sh --required-thing some_thingy --boolean-thing
 
 Because cmdarg does key off of the short options, you are limited to as many unique single characters are in your character set (likely 61 - 26 lower & upper alpha, +9 numerics).
 
@@ -169,8 +179,8 @@ You can use the cmdarg function to accept arrays and hashes from the command lin
 
     declare -a array
     declare -A hash
-    cmdarg 'a:[]' 'array' 'Some array you can set indexes in'
-    cmdarg 'H:{}' 'hash' 'Some hash you can set keys in'
+    cmdarg 'a?[]' 'array' 'Some array you can set indexes in'
+    cmdarg 'H?{}' 'hash' 'Some hash you can set keys in'
 
 
     your_script -a 32 --array something -H key=value --hash other_key=value
@@ -206,4 +216,4 @@ cmdarg does not use getopt or getopts for option parsing. Its parser is written
 Tests
 =====
 
-cmdarg is testable by the shunit bash unit testing tool. See the tests/ directory.
+cmdarg is testable by the shunit bash unit testing tool (https://www.github.com/akesterson/shunit/). See the tests/ directory.
diff --git a/cmdarg.sh b/cmdarg.sh
index 761abc2..a099ed3 100644
--- a/cmdarg.sh
+++ b/cmdarg.sh
@@ -8,7 +8,8 @@ fi
 
 
 CMDARG_FLAG_NOARG=0
-CMDARG_FLAG_WITHARG=1
+CMDARG_FLAG_REQARG=1
+CMDARG_FLAG_OPTARG=2
 
 CMDARG_TYPE_ARRAY=1
 CMDARG_TYPE_HASH=2
@@ -42,8 +43,12 @@ function cmdarg
 	exit 1
     fi
 
-    if [[ "${1:1:1}" == ":" ]]; then
-	CMDARG_FLAGS[$shortopt]=$CMDARG_FLAG_WITHARG
+    declare -xA argtypemap
+    argtypemap[':']=$CMDARG_FLAG_REQARG
+    argtypemap['?']=$CMDARG_FLAG_OPTARG
+    argtype=${1:1:1}
+    if [[ "$argtype" != "" ]]; then
+	CMDARG_FLAGS[$shortopt]=${argtypemap["$argtype"]}
 	if [[ "${1:2:4}" == "[]" ]]; then
 	    declare -p ${key} >/dev/null 2>&1
 	    if [[ $? -ne 0 ]]; then
@@ -71,7 +76,7 @@ function cmdarg
     CMDARG_REV["$2"]=$shortopt
     CMDARG_DESC["$shortopt"]=$3
     CMDARG_DEFAULT["$shortopt"]=${4:-}
-    if [[ ${CMDARG_FLAGS[$shortopt]} -eq $CMDARG_FLAG_WITHARG ]] && [[ "${4:-}" == "" ]]; then
+    if [[ ${CMDARG_FLAGS[$shortopt]} -eq $CMDARG_FLAG_REQARG ]] && [[ "${4:-}" == "" ]]; then
 	CMDARG_REQUIRED+=($shortopt)
     else
 	CMDARG_OPTIONAL+=($shortopt)
@@ -258,7 +263,7 @@ function cmdarg_parse
     	    exit 1
     	fi
 
-	if [[ ${CMDARG_FLAGS[$opt]} -eq $CMDARG_FLAG_WITHARG ]]; then
+	if [[ ${CMDARG_FLAGS[$opt]} -eq $CMDARG_FLAG_REQARG ]] || [[ ${CMDARG_FLAGS[$opt]} -eq ${CMDARG_FLAG_OPTARG} ]]; then
 	    optarg=$1
 	    shift
 	fi