A T cell activating bispecific antigen binding molecule comprising (a) a first antigen binding moiety which specifically binds to CD19, wherein the first antigen binding moiety is a conventional Fab molecule; (b) a second antigen binding moiety which specifically binds to CD3, wherein the second antigen binding moiety is a crossover Fab molecule wherein the variable domains VL and VH of the Fab light chain and the Fab heavy chain are replaced by each other; (c) a third antigen binding moiety which specifically binds to CD19, wherein the first antigen binding moiety is a conventional Fab molecule; (d) an Fc domain composed of a first and a second subunit capable of stable association; wherein in the first and the third antigen binding moiety in the constant domain CL the amino acid at position 124 is substituted independently by lysine, arginine or histidine, numbering according to Kabat, and the amino acid at position 123 is substituted independently by lysine, arginine or histidine, numbering according to Kabat, and in the constant domain CH1 the amino acid at position 147 is substituted independently by glutamic acid, or aspartic acid, numbering according to Kabat EU index, and the amino acid at position 213 is substituted independently by glutamic acid, or aspartic acid, numbering according to Kabat EU index; and wherein the first and the third antigen binding moiety comprise a heavy chain variable region, particularly a humanized heavy chain variable region, comprising the heavy chain complementarity determining region (HCDR) 1 of SEQ ID NO: 14, the HCDR 2 of SEQ ID NO: 15 and the HCDR 3 of SEQ ID NO: 16, and a light chain variable region, particularly a humanized light chain variable region, comprising the light chain complementarity determining region (LCDR) 1 of SEQ ID NO: 17, the LCDR 2 of SEQ ID NO: 18 and the LCDR 3 of SEQ ID NO: 19; and wherein (i) the second and the third antigen binding moiety are each fused at the C-terminus of the Fab heavy chain to the N-terminus of one of the subunits of the Fc domain, and the first antigen binding moiety is fused at the C-terminus of the Fab heavy chain to the N-terminus of the Fab heavy chain of the second antigen binding moiety, or (ii) the first and the third antigen binding moiety are each fused at the C-terminus of the Fab heavy chain to the N-terminus of one of the subunits of the Fc domain, and the second antigen binding moiety is fused at the C-terminus of the Fab heavy chain to the N-terminus of the Fab heavy chain of the first antigen binding moiety. (a) a first antigen binding moiety which specifically binds to CD19, wherein the first antigen binding moiety is a conventional Fab molecule; (b) a second antigen binding moiety which specifically binds to CD3, wherein the second antigen binding moiety is a crossover Fab molecule wherein the variable domains VL and VH of the Fab light chain and the Fab heavy chain are replaced by each other; (c) a third antigen binding moiety which specifically binds to CD19, wherein the first antigen binding moiety is a conventional Fab molecule; (d) an Fc domain composed of a first and a second subunit capable of stable association; wherein in the first and the third antigen binding moiety in the constant domain CL the amino acid at position 124 is substituted independently by lysine, arginine or histidine, numbering according to Kabat, and the amino acid at position 123 is substituted independently by lysine, arginine or histidine, numbering according to Kabat, and in the constant domain CH1 the amino acid at position 147 is substituted independently by glutamic acid, or aspartic acid, numbering according to Kabat EU index, and the amino acid at position 213 is substituted independently by glutamic acid, or aspartic acid, numbering according to Kabat EU index; and wherein the first and the third antigen binding moiety comprise a heavy chain variable region, particularly a humanized heavy chain variable region, comprising the heavy chain complementarity determining region (HCDR) 1 of SEQ ID NO: 14, the HCDR 2 of SEQ ID NO: 15 and the HCDR 3 of SEQ ID NO: 16, and a light chain variable region, particularly a humanized light chain variable region, comprising the light chain complementarity determining region (LCDR) 1 of SEQ ID NO: 17, the LCDR 2 of SEQ ID NO: 18 and the LCDR 3 of SEQ ID NO: 19; and wherein (i) the second and the third antigen binding moiety are each fused at the C-terminus of the Fab heavy chain to the N-terminus of one of the subunits of the Fc domain, and the first antigen binding moiety is fused at the C-terminus of the Fab heavy chain to the N-terminus of the Fab heavy chain of the second antigen binding moiety, or (ii) the first and the third antigen binding moiety are each fused at the C-terminus of the Fab heavy chain to the N-terminus of one of the subunits of the Fc domain, and the second antigen binding moiety is fused at the C-terminus of the Fab heavy chain to the N-terminus of the Fab heavy chain of the first antigen binding moiety.