This invention pertains to certain carbamic acid compounds which inhibit HDAC (histone deacetylase) activity of the following formula:[Insert formula]wherein: Cy is independently a cyclyl group; Q1 is independently a covalent bond or cyclyl leader group; the piperazin-1,4-diyl group is optionally substituted; J1 is independently a covalent bond or -C(=O)- ; J2 is independently -C(=O)- or -S(=O)2- ; Q2 is independently an acid leader group; wherein: Cy is independently: C3-20carbocyclyl, C3-20heterocyclyl, or C5-20aryl; and is optionally substituted; Q1 is independently: a covalent bond; C1-7alkylene; or C1-7alkylene-X-C1-7alkylene, -X-C1-7alkylene, or C1-7alkylene-X-, wherein X is -O- or -S-; and is optionally substituted; Q2 is independently: C4-8alkylene; and is optionally substituted; and has a backbone length of at least 4 atoms; or: Q2 is independently: C5-20arylene; C5-20arylene-C1-7alkylene; C1-7alkylene-C5-20arylene; or, C1-7alkylene-C5-20arylene-C1-7alkylene; and is optionally substituted; and has a backbone length of at least 4 atoms; or a pharmaceutically acceptable salt, solvate, amide, ester, ether, chemically protected form, or prodrug thereof. The present invention also pertains to pharmaceutical compositions comprising such compounds, and the use of such compounds and compositions, both in vitro and in vivo, to inhibit HDAC, and in the treatment of conditions mediated by HDAC, cancer, proliferative conditions, psoriasis, etc.