Thisvolumecontainspapersselectedforpresentationatthe28thSymposiumon MathematicalFoundationsofComputerScience-MFCS2003,heldinBratislava, Slovakia, August 25-29, 2003. MFCS 2003 was organized by the Slovak Society for Computer Science and the Comenius University in Bratislava, in cooperation with other institutions in Slovakia. It was supported by the European Association for Theoretical C- puter Science and the Slovak Research Consortium for Informatics and Mat- matics. The series of MFCS symposia, organized alternately in the Czech Republic, PolandandSlovakiasince1972,hasawell-establishedtradition. TheMFCSs- posiaencouragehigh-qualityresearchinallbranchesoftheoreticalcomputers- ence. Theirbroadscopeprovidesanopportunitytobringtogetherspecialistswho donotusuallymeetatspecializedconferences. Thepreviousmeetingstookplace ? in Jablonna, 1972; Strbsk' e Pleso, 1973; Jadwisin, 1974; Mari' ansk'eL' azn? e, 1975; Gdansk, ' 1976; Tatransk' a Lomnica, 1977; Zakopane, 1978; Olomouc, 1979; Ry- ? dzina, 1980; Strbsk' e Pleso, 1981; Prague, 1984; Bratislava, 1986; Carlsbad, 1988; Porabk , a-Kozubnik,1989;Bansk' aBystrica,1990;KazimierzDolny,1991;Prague, 1992;Gdansk, ' 1993,Ko? sice,1994;Prague,1995;Krak' ow,1996;Bratislava,1997; Brno, 1998; Szklarska Por, eba, 1999; Bratislava, 2000; Mari' ansk'eL' azn?e, 2001; and Warsaw-Otwock, 2002. The MFCS 2003 Proceedings consists of 7 invited papers and 55 c- tributed papers. The latter were selected by the Program Committee from a total of 137 submitted papers.