For information on visa requirements, see Visas.
The only viable border crossing from these two countries into Colombia is via Leticia in the far southeastern corner of the Colombian Amazon. Leticia is reached from Iquitos (Peru) and Manaus (Brazil) by riverboat. Flights are the only way to get from Leticia to other parts of Colombia.
Virtually all travelers use the Carretera Panamericana border crossing through Tulcán (Ecuador) and Ipiales (Colombia). The part of the Panamericana between Pasto and Popayán has improved but to avoid problems altogether and enjoy fantastic views, it's best to travel this road during the day.
Another option is the crossing at San Miguel in Putumayo to Nueva Loja (Lago Agrio) in the Ecuadorean Amazon. Backpackers were safely using this route at the time of research, but check the situation on the ground with your hotel before proceeding, as this area fluctuates often between acceptable and sketchy. Always travel by day on this route.
The political crisis in Venezuela has led to the borders with Colombia operating irregularly. At times the government in Caracas has closed the borders completely while on other occasions they have been closed to vehicle traffic. Check the latest news before making plans.
It is important to note that government travel advice in the UK, US, Canada and numerous other countries currently advises against all non-essential travel to Venezuela, in particular to areas along its 2219km-long border with Colombia.
There are four border crossings between Colombia and Venezuela. Traditionally the most popular with travelers is the route via San Antonio del Táchira (Venezuela) and Cúcuta (Colombia), on the main Caracas–Bogotá road.
There is another reasonably popular border crossing at Paraguachón, on the Maracaibo (Venezuela) to Maicao (Colombia) road. Buses and shared taxis run between Maracaibo and Maicao. Both Colombian and Venezuelan officials at the border will stamp your passport.
Not so popular is the crossing from Colombia's Puerto Carreño and either Puerto Páez or Puerto Ayacucho (both in Venezuela). Still less useful is the crossing from El Amparo de Apure (Venezuela) to Arauca (Colombia), a remote and somewhat insecure region.
At the time of research there are no direct buses operating between Colombian and Venezuelan cities.
Considering how cheap and extensive bus transportation is in Colombia, and the costs involved in shipping a vehicle to South America, there is little reason to bring your own vehicle unless you are on a multicountry odyssey.