When a tenant is not complying with the terms of a rental agreement, a landlord determine that it's necessary to institute legal eviction proceedings. The UD-100 form is the one used in an unlawful detainer action (commonly referred to as an eviction lawsuit) in California. This form is typically filed after the landlord has served the tenant with the appropriate notice, such as: - A 3-day notice to pay rent or quit - A 30-day notice to vacate - A 60-day notice to vacate - A 3-day notice to perform covenants or quit These notices are prerequisites to filing the UD-100 to ensure that the tenant is given a proper notice and cure period to comply or vacate the property. Once the notice period expires, if the tenant remains in possession of the property and does not comply with the lease, then serving the complaint through the UD-100 form allows the landlord to seek legal possession and potentially pursue other damages or costs incurred. Therefore, the need for this form is "triggered" by the tenant's failure to respond appropriately to the notice(s) issued, commencing formal eviction proceedings in court.