Medicament mixing and injection apparatus comprising: an injection needle assembly including a needle extending along an injection axis and a needle base to which said needle is fixed centrally to the injection needle assembly along the injection axis; a syringe attachment element configured at a first axial end thereof to receive a needleless syringe and a second axial end thereof to engage said needle base in at least first and second relative engagement orientations which are mutually axially separated along said injection axis; and a medicament mixing chamber engagement assembly including: an intermediate portion having a hand-engageable portion, said intermediate portion including a needle chamber surrounding said needle and a first liquid conduit portion, sealed from said needle chamber; and a medicament mixing chamber engagement portion including a second liquid conduit portion communicating with said first liquid conduit portion and configured for communication with a medicament mixing chamber, said syringe attachment element and said needle base being configured to: (i) when said syringe attachment element and said needle base are in said first relative engagement orientation, permit liquid communication between an interior of said needleless syringe and said first liquid conduit portion and prevent liquid communication between the interior of the needleless syringe and the needle, and (ii) when said syringe attachment element and said needle base are relatively axially displaced along said injection axis such that said syringe attachment element and said needle base are in said second relative engagement orientation, permit liquid communication between an interior of said needleless syringe and said needle and prevent liquid communication between the interior of the needleless syringe and the first liquid conduit portion, the second relative engagement orientation being axially separated from said first relative engagement orientation along said injection axis. an injection needle assembly including a needle extending along an injection axis and a needle base to which said needle is fixed centrally to the injection needle assembly along the injection axis; a syringe attachment element configured at a first axial end thereof to receive a needleless syringe and a second axial end thereof to engage said needle base in at least first and second relative engagement orientations which are mutually axially separated along said injection axis; and a medicament mixing chamber engagement assembly including: an intermediate portion having a hand-engageable portion, said intermediate portion including a needle chamber surrounding said needle and a first liquid conduit portion, sealed from said needle chamber; and a medicament mixing chamber engagement portion including a second liquid conduit portion communicating with said first liquid conduit portion and configured for communication with a medicament mixing chamber, an intermediate portion having a hand-engageable portion, said intermediate portion including a needle chamber surrounding said needle and a first liquid conduit portion, sealed from said needle chamber; and a medicament mixing chamber engagement portion including a second liquid conduit portion communicating with said first liquid conduit portion and configured for communication with a medicament mixing chamber, said syringe attachment element and said needle base being configured to: (i) when said syringe attachment element and said needle base are in said first relative engagement orientation, permit liquid communication between an interior of said needleless syringe and said first liquid conduit portion and prevent liquid communication between the interior of the needleless syringe and the needle, and (ii) when said syringe attachment element and said needle base are relatively axially displaced along said injection axis such that said syringe attachment element and said needle base are in said second relative engagement orientation, permit liquid communication between an interior of said needleless syringe and said needle and prevent liquid communication between the interior of the needleless syringe and the first liquid conduit portion, the second relative engagement orientation being axially separated from said first relative engagement orientation along said injection axis. (i) when said syringe attachment element and said needle base are in said first relative engagement orientation, permit liquid communication between an interior of said needleless syringe and said first liquid conduit portion and prevent liquid communication between the interior of the needleless syringe and the needle, and (ii) when said syringe attachment element and said needle base are relatively axially displaced along said injection axis such that said syringe attachment element and said needle base are in said second relative engagement orientation, permit liquid communication between an interior of said needleless syringe and said needle and prevent liquid communication between the interior of the needleless syringe and the first liquid conduit portion, the second relative engagement orientation being axially separated from said first relative engagement orientation along said injection axis.