H eavy quark physi cs o ers a uni que opportuni ty to expl ore the avour structure of the Standard M odel .T he thi rd fam i l y ofquarksi sthe l essknow n. Itsup-type quark, the top,hasnotyetbeen observed,al though we are getti ng m ore and m ore stri ngent l i m i ts on i ts m ass from di rect search and radi ati ve correcti on anal ysi s. O n the other hand, the correspondi ng dow n-type quark, the b, i s bei ng studi ed w i th i ncreasi ng accuracy. Both grow i ng stati sti cs and the operati on ofdedi cated vertex detector for btaggi ng athi gh energy m achi nesal ready al l ow sa good determ i nati on ofbcoupl i ngs. Present **data** cl earl y poi ntto the b asthe I 3 = {1/2 com ponent ofa weak l eft-handed i sodoubl et [ 1] .