It would seem: std::string foo = boost::algorithm::to_lower_copy< std::string >( "bar" ); isn't valid. Instead one has to do for example: std::string foo = boost::algorithm::to_lower_copy( std::string( "bar" ) ), which while perhaps just as terse and natural creates an extra unneeded temporary. I propose the following addition, as well as one for to_upper_copy: template<typename OutputSequenceT, typename RangeT> inline OutputSequenceT to_lower_copy( const RangeT& Input, const std::locale& Loc=std::locale()) { OutputSequenceT Output( ::boost::begin( Input ), ::boost::end( Input ) ); ::boost::algorithm::detail::transform_range( ::boost::as_literal( Output ), ::boost::algorithm::detail::to_lowerF< typename range_value<OutputSequenceT>::type >(Loc)); return Output; } Or perhaps I've missed something altogether :) Kind regards, Sebastian Karlsson