This book provides comprehensive knowledge about thyroid gland and highlights the recent trends in the management of thyroid dysfunctions. Thyroid disorders are amongst the most prevalent of medical conditions possibly after diabetes. The prevalence of thyroid dysfunction in adults in the general population ranges from 1 to 10 percent, and is even higher in selected groups. In the United Kingdom, 1–2% of the adult population is found to have thyroid dysfunction. It is interesting to note that thyroxin is the sixth most commonly dispensed drug in Scotland. Virtually all studies report higher prevalence rates for hypothyroidism in women and with advancing age.  Abnormal thyroid functions have important public health consequences. Suppressed TSH levels have been associated with decreased bone density and with an increased risk of atrial fibrillation and premature atrial beat. It has been known for decades that overt hypothyroidism contributes to elevated serum cholesterol levels and cardiovascular risk and recent studies suggest this may also be true with subclinical hypothyroidism​.