Process for preparing ethylenebis(alkylphosphinic) acids, esters and salts, which comprises a) reacting a phosphinic acid source with olefins in the presence of a catalyst A to give an alkylphosphonous acid, or salt or ester thereof, b) reacting the alkylphosphonous acid, or salt or ester thereof, thus formed with an acetylenic compound in the presence of a catalyst B to give the ethylenebis(alkylphosphinic) acid derivative where R 1, R 2, R 3, R 4, R 5, R 6, R 11, R 12, R 13, R 14 are the same or different and are each independently H, C 1 -C 18 -alkyl, C 6 -C 18 -aryl, C 6 -C 18 -aralkyl, C 6 -C 18 -alkylaryl, where the C 6 -C 18 -aryl, C 6 -C 18 -aralkyl, C 6 -C 18 -alkylaryl groups may be substituted by -C CH 3, OH, CH 2 OH, NH 2, NO 2, OCH 3, SH and/or OC CH 3, and X is Mg, Ca, Al, Sb, Sn, Ge, Ti, Fe, Zr, Zn, Ce, Bi, Sr, Mn, Cu, Ni, Li, Na, K, H and/or a protonated nitrogen base, and/or is H, C 1 -C 18 -alkyl, C 6 -C 18 -aryl, C 6 -C 18 -aralkyl, C 6 -C 18 -alkylaryl, (CH 2) k OH, CH 2 -CHOH-CH 2 OH, (CH 2) k O(CH 2) 1 H, (CH 2) k -CH - (CH 2) 1 H, (CH 2 -CH 2 O) k H, (CH 2 -C[CH 3]HO) k H, (CH 2 -C[CH 3]HO) k (CH 2 -CH 2 O) 1 H, (CH 2 -CH 2 O) k (CH 2 -C[CH 3]HO)H, (CH 2 -CH 2 O) k -alkyl, (CH 2 -C[CH 3]HO) k -alkyl, (CH 2 -C[CH 3]HO) k (CH 2 -CH 2 O) 1 -alkyl, (CH 2 -CH 2 O) k (CH 2 -C[CH 3]HO)O-alkyl, (CH 2) k NH 2, (CH 2) k N[(CH 2) 1 H] 2, where k and 1 are the same or different and are each independently an integer from 0 to 20, and m is 1 to 4, and the catalyst A comprises transition metals and/or transition metal compounds and/or catalyst systems composed of a transition metal and/or a transition metal compound and at least one ligand, and the catalyst B comprises electromagnetic radiation. a) reacting a phosphinic acid source with olefins in the presence of a catalyst A to give an alkylphosphonous acid, or salt or ester thereof, b) reacting the alkylphosphonous acid, or salt or ester thereof, thus formed with an acetylenic compound in the presence of a catalyst B to give the ethylenebis(alkylphosphinic) acid derivative where R 1, R 2, R 3, R 4, R 5, R 6, R 11, R 12, R 13, R 14 are the same or different and are each independently H, C 1 -C 18 -alkyl, C 6 -C 18 -aryl, C 6 -C 18 -aralkyl, C 6 -C 18 -alkylaryl, where the C 6 -C 18 -aryl, C 6 -C 18 -aralkyl, C 6 -C 18 -alkylaryl groups may be substituted by -C CH 3, OH, CH 2 OH, NH 2, NO 2, OCH 3, SH and/or OC CH 3, and X is Mg, Ca, Al, Sb, Sn, Ge, Ti, Fe, Zr, Zn, Ce, Bi, Sr, Mn, Cu, Ni, Li, Na, K, H and/or a protonated nitrogen base, and/or is H, C 1 -C 18 -alkyl, C 6 -C 18 -aryl, C 6 -C 18 -aralkyl, C 6 -C 18 -alkylaryl, (CH 2) k OH, CH 2 -CHOH-CH 2 OH, (CH 2) k O(CH 2) 1 H, (CH 2) k -CH - (CH 2) 1 H, (CH 2 -CH 2 O) k H, (CH 2 -C[CH 3]HO) k H, (CH 2 -C[CH 3]HO) k (CH 2 -CH 2 O) 1 H, (CH 2 -CH 2 O) k (CH 2 -C[CH 3]HO)H, (CH 2 -CH 2 O) k -alkyl, (CH 2 -C[CH 3]HO) k -alkyl, (CH 2 -C[CH 3]HO) k (CH 2 -CH 2 O) 1 -alkyl, (CH 2 -CH 2 O) k (CH 2 -C[CH 3]HO)O-alkyl, (CH 2) k NH 2, (CH 2) k N[(CH 2) 1 H] 2, where k and 1 are the same or different and are each independently an integer from 0 to 20, and m is 1 to 4, and the catalyst A comprises transition metals and/or transition metal compounds and/or catalyst systems composed of a transition metal and/or a transition metal compound and at least one ligand, and the catalyst B comprises electromagnetic radiation. R 1, R 2, R 3, R 4, R 5, R 6, R 11, R 12, R 13, R 14 are the same or different and are each independently H, C 1 -C 18 -alkyl, C 6 -C 18 -aryl, C 6 -C 18 -aralkyl, C 6 -C 18 -alkylaryl, where the C 6 -C 18 -aryl, C 6 -C 18 -aralkyl, C 6 -C 18 -alkylaryl groups may be substituted by -C CH 3, OH, CH 2 OH, NH 2, NO 2, OCH 3, SH and/or OC CH 3, and X is Mg, Ca, Al, Sb, Sn, Ge, Ti, Fe, Zr, Zn, Ce, Bi, Sr, Mn, Cu, Ni, Li, Na, K, H and/or a protonated nitrogen base, and/or is H, C 1 -C 18 -alkyl, C 6 -C 18 -aryl, C 6 -C 18 -aralkyl, C 6 -C 18 -alkylaryl, (CH 2) k OH, CH 2 -CHOH-CH 2 OH, (CH 2) k O(CH 2) 1 H, (CH 2) k -CH - (CH 2) 1 H, (CH 2 -CH 2 O) k H, (CH 2 -C[CH 3]HO) k H, (CH 2 -C[CH 3]HO) k (CH 2 -CH 2 O) 1 H, (CH 2 -CH 2 O) k (CH 2 -C[CH 3]HO)H, (CH 2 -CH 2 O) k -alkyl, (CH 2 -C[CH 3]HO) k -alkyl, (CH 2 -C[CH 3]HO) k (CH 2 -CH 2 O) 1 -alkyl, (CH 2 -CH 2 O) k (CH 2 -C[CH 3]HO)O-alkyl, (CH 2) k NH 2, (CH 2) k N[(CH 2) 1 H] 2, where k and 1 are the same or different and are each independently an integer from 0 to 20, and m is 1 to 4,