The purpose of this study is to determine whether a compound known as LY2422347 is effective in treating people diagnosed with primary insomnia (difficulty sleeping with no other significant contributing factor, such as depression).

Inclusion Criteria:

• must have been diagnosed with primary insomnia
• must not be significantly overweight
• must be able to visit the study doctor's office once every 2 weeks for 8 weeks and willing to use a handheld electronic device as a sleep diary every day
• must be able to read and speak in English and be able to see well enough to use the handheld electronic device
• the patient's answer to the question "During the past month, how would you rate your sleep quality overall?" must be either "Very Bad" or "Fairly Bad"

Exclusion Criteria:

• cannot have a clinically significant and/or uncontrolled condition or other significant ailment including restless leg syndrome (RLS) or periodic limb movement disorder (PLMD)
• cannot have obstructive sleep apnea (OSA), or be considered by the study doctor to have probable OSA based upon patient history and physical examination
• cannot be currently using antidepressants, antipsychotics, stimulants, antihistaminics, or other medications that are known to effect sleep
• cannot have a current or previous major psychiatric disorder (other than insomnia) such as depression, schizophrenia, bipolar disorder, social anxiety, or another psychotic disorder.