You own a nice piece of property and you don't want it getting ruined; or, you've sunk a lot of money into buy an apartment building and you're counting on the rent money to pay for the mortgage. How are landlords protected from destructive tenants or from those who don't pay? If a tenant isn't adhering to the terms of the rental contract regarding his responsibilities for taking care of the apartment, refraining from bringing in pets (if the contract had specified that pets weren't allowed), or if he's neglecting to pay rent, the landlord has the right to start eviction proceedings against the tenant to get him out.
A landlord has the right to collect rent, according to the schedule that was set up in the lease with the tenant (weekly, monthly, etc.), and the landlord can raise the amount of rent when the lease expires, unless the building is an older one that is rent-controlled (also called rent-stabilized). These buildings are more common in the largest U.S. cities. The landlord has the right to go into his property, but only with certain conditions. For example, if he wants to repair something, he usually has to give notice of when he'll be coming, unless it's an emergency (fire, flood, major storm damage). If the tenant hasn't paid rent despite having received written notices, the landlord is allowed to enter the apartment to demand that the rent be paid.
On the other hand, along with landlord rights comes responsibility. The landlord has the responsibility to stay on top of any repairs so the tenant is living in a safe environment. The landlord is responsible to make sure that the tenants aren't criminals who will negatively affect the neighborhood, and the landlord may not discriminate when choosing tenants.