Rings --- Also known as Schatzki rings from the discoverer, these rings are usually mucosal rings rather than muscular rings, and are located near the gastroesophageal junction at the squamo-columnar junction. Presence of multiple rings may suggest eosinophilic esophagitis. Rings cause intermittent mechanical dysphagia, meaning patients will usually present with transient discomfort and regurgitation while swallowing solids and then liquids, depending on the constriction of the ring. Webs --- Usually squamous mucosal protrusion into the esophageal lumen, especially anterior cervical esophagus behind the cricoid area. Patients are usually asymptomatic or have intermittent dysphagia. An important association of esophageal webs is to the Plummer–Vinson syndrome in iron deficiency, in which case patients will also have anemia, koilonychia, fatigue, and other symptoms of anemia. Achalasia is an idiopathic motility disorder characterized by failure of lower esophageal sphincter (LES) relaxation as well as loss of peristalsis in the distal esophagus, which is mostly smooth muscle. Both of these features impair the ability of the esophagus to empty contents into the stomach. Patients usually complain of dysphagia to both solids and liquids. Dysphagia to liquids, in particular, is a characteristic of achalasia. Other symptoms of achalasia include regurgitation, night coughing, chest pain, weight loss, and heartburn. The combination of achalasia, adrenal insufficiency, and alacrima (lack of tear production) in children is known as the triple-A (Allgrove) syndrome. In most cases the cause is unknown (idiopathic), but in some regions of the world, achalasia can also be caused by Chagas disease due to infection by Trypanosoma cruzi.
Scleroderma is a disease characterized by atrophy and sclerosis of the gut wall, most commonly of the distal esophagus (~90%). Consequently, the lower esophageal sphincter cannot close and this can lead to severe gastroesophageal reflux disease (GERD). Patients typically present with progressive dysphagia to both solids and liquids secondary to motility problems or peptic stricture from acid reflux. Spastic motility disorders include diffuse esophageal spasm (DES), nutcracker esophagus, hypertensive lower esophageal sphincter, and nonspecific spastic esophageal motility disorders (NEMD). DES can be caused by many factors that affect muscular or neural functions, including acid reflux, stress, hot or cold food, or carbonated drinks. Patients present with intermittent dysphagia, chest pain, or heartburn.Rare causes of esophageal dysphagia not mentioned above

Diverticulum
Aberrant subclavian artery, or (dysphagia lusoria)
Cervical osteophytes
Enlarged aorta
Enlarged left atrium
Mediastinal tumor

Diagnostic tools
Once a patient complains of dysphagia they should have an upper endoscopy (EGD). Commonly patients are found to have esophagitis and may have an esophageal stricture. Biopsies are usually done to look for evidence of esophagitis even if the EGD is normal. Usually no further testing is required if the diagnosis is established on EGD. Repeat endoscopy may be needed for follow up. If there is a suspicion of a proximal lesion such as:

history of surgery for laryngeal or esophageal cancer
history of radiation or irritating injury
achalasia
Zenkers diverticuluma barium swallow may be performed before endoscopy to help identify abnormalities that might increase the risk of perforation at the time of endoscopy.