Hello all, a friend of mine helped me figure it out.    libname IPUMS "/folders/myfolders/datafile/usa_00002.dat/"; filename ASCIIDAT "/folders/myfolders/datafile/usa_00002.dat/usa_00002.dat"; So the only difference between the statements is that the libname includes the filepath up until the actual datafile name, while filename includes the filepath and the datafile name. I hope this helps out anyone else in the future!  ... View more