Science fiction has the distinct advantage and disadvantage of being one of the most elaborate, expensive, and sometimes unintentionally humorous genres in filmmaking history. It has been in existence since 1902, when Georges Méliès made From the Earth to the Moon (Le Voyage dans la lune), based on the Jules Verne novel. This was followed by Fritz Lang's 1927 masterpiece Metropolis. From that time on, science fiction became a motion picture mainstay, and filmmakers have taken all kinds of creative and technological risks with varying degrees of success.

The science fiction genre covers a wide range of subgenres, each with its own challenges, charm, budgetary limitations, and audience appeal. There's also a certain amount of confusion about films that on first glance appear to be sci-fi, but also cross into other genres, like horror or fantasy. The debate still continues over the 1979 film Alien, which is alternately classified as a sci-fi or horror film. Regardless, there are a host of categories from which to choose when writing and filming sci-fi:

• Alien Invasions (Earth vs. the Flying Saucers, War of the Worlds, Invasion of the Body Snatchers, Independence Day, The Abyss, Men in Black, Contact)

• Disasters (The Day the Earth Stood Still, When Worlds Collide, Armageddon, Deep Impact, The Day after Tomorrow)

• Viruses Run Amok (The Andromeda Strain, The Omega Man, Resident Evil)

• Post-Apocalyptic Worlds (Soylent Green, Terminator, Mad Max, Road Warrior, Starship Troopers, Blade Runner, The Matrix, Strange Days)

• Hero's Journeys (Star Wars, Forbidden Planet, Outland, The Fifth Element, Back to the Future, Planet of the Apes)

• Outer Space Excursions (2001: A Space Odyssey, 2010, The Martian Chronicles, Alien, Red Planet, Solaris, Event Horizon, Star Trek)

• Technological Rebellion (Westworld, Gattaca, The Stepford Wives, Total Recall)

• Genetic Mutants Gone Horribly Wrong (It Came from Beneath the Sea, The Deadly Mantis, The Fly, The Island of Dr. Moreau)

Sci-fi fans are die-hard dreamers who will often watch anything remotely alien, robotic, time disoriented, mind altered, and genetically mutated. Sci-fi films typically require not only a brilliant script but a huge budget, as in the case of Aliens, Independence Day, Armageddon, Contact, the Jurassic Park, Matrix, and Terminator trilogies, and the Star Wars franchise. If you're writing or considering filming a science fiction masterpiece, your overwhelming concern should be budget. It's easy to get carried away when you're dealing with the high-end special effects and technical wizardry necessary to create a blockbuster hit.