Make sure to have the Clib generated in the related cURL library - if you use EiffelStudio >= 7.0 check %ISE_LIBRARY%\library\cURL\spec\%ISE_C_COMPILER%\$ISE_PLATFORM or $ISE_LIBRARY/library/cURL/spec/$ISE_PLATFORM - otherwise if you use earlier version check under ext/ise_library/curl/spec/... And on Windows, be sure to get the libcurl.dll from %ISE_LIBRARY%\studio\spec\%ISE_PLATFORM%\bin\libcurl.dll