Updated October 4th: Here are the Scott Catalogue numbers:

5106 Puppy
5107 Betta fish
5108 Iguana
5109 Hamster
5110 Goldfish
5111 Kitten
5112 Rabbit
5113 Tortoise
5114 Guinea pig
5115 Parrot
5116 Corn snake
5117 Mouse
5118 Hermit crab
5119 Chinchilla
5120 Gerbil
5121 Gecko
5122 Cat
5123 Horse
5124 Parakeets
5125 Dog
a. Convertible booklet pane of 20, #5106-5125

Updated July 7, 2016:
On August 2, 2016, in Las Vegas, NV, the U.S. Postal Service® will issue the Pets stamps (Forever® priced at 47 cents) in 20 designs, in a pressure-sensitive adhesive (PSA) double-sided booklet of 20 stamps (Item 680700).

The stamps will go on sale nationwide August 2, 2016.

With this booklet of 20 stamps, the U.S. Postal Service celebrates the animals in our lives that bring us joy, companionship, and love. The stamp art features existing photographs of different animals taken against white backgrounds. Each photograph represents animals from these groups: puppies, betta fish, iguanas, hamsters, goldfish, parrots, guinea pigs, tortoises, rabbits, kittens, corn snakes, mice, hermit crabs, chinchillas, gerbils, dogs, parakeets, horses, cats, and geckos. Art director Derry Noyes designed the stamps with existing photographs by Eric Isselée.

Stamp Fulfillment Services will make an automatic push distribution to Post Offices of a quantity to cover approximately 30 days of sales.

How to Order the First-Day-of-Issue Postmark:
Customers have 60 days to obtain the first-day-of-issue postmark by mail. They may purchase new stamps at their local Post Office, at The Postal Store® website at http: ⁄⁄www.usps.com⁄shop, or by calling 800-782-6724. They should affix the stamps to envelopes of their choice, address the envelopes (to themselves or others), and place them in a larger envelope addressed to:

Pets Stamps
United States Postal Service
Attn: Marilyn Wassell
1001 East Sunset Road, #2009
Las Vegas, NV 89199-9998

After applying the first-day-of-issue postmark, the Postal Service™ will return the envelopes through the mail. There is no charge for the postmark up to a quantity of 50. There is a 5-cent charge for each additional postmark over 50. All orders must be postmarked by October 2, 2016.

There are five philatelic products for this stamp issue:

• 680706, Press Sheet with Die-cut, $75.20
• 680710 Digital Color Postmark Keepsake (random single), $11.95
• 680716 First-Day Cover (Set of 20), $18.20
• 680721 Digital Color Postmark (Set of 20), $32.40
• 680730 Ceremony Program (random single), $6.95

Technical Specifications:

Issue: Pets Stamps
Item Number: 680700
Denomination & Type of Issue: First-Class Mail Forever
Format: Double-Sided Booklet of 20
Series: N⁄A
Issue Date & City: August 2, 2016, Las Vegas, NV 89119
Art Director: Derry Noyes, Washington, DC
Designer: Derry Noyes, Washington, DC
Typographer: Derry Noyes, Washington, DC
Existing Photos: Eric Isselée
Modeler: Joseph Sheeran
Manufacturing Process: Offset
Printer: Ashton Potter (USA) Ltd. (APU)
Printed at: Williamsville, NY
Press Type: Muller A76
Stamps per Booklet: 20
Print Quantity: 400,000,000 stamps
Paper Type: Nonphosphored Type III, Block Tag
Adhesive Type: Pressure-sensitive
Processed at: Ashton Potter (USA) Ltd. (APU)
Stamp Orientation: Horizontal
Image Area (w x h): 1.05 x 0.77 in.⁄26.67 x 19.56 mm
Stamp Size (w x h): 1.19 x 0.91 in.⁄30.23 x 23.11 mm
Full Booklet Size (w x h): 2.38 x 5.76 in.⁄60.45 x 146.30 mm
Press Sheet Size (w x h): 23.29 x 4.76 in.⁄ 591.57 x 120.90 mm
Colors: Black, Cyan, Magenta, Yellow
Plate Size: 880 stamps per revolution
Plate Numbers: “P” followed by four (4) single digits
Marginal Markings:
Header. “Pets” • Twenty First-Class Forever Stamps • Plate numbers in peel strip area • © 2015 • USPS Logo • Promotional Text in peel strip area

Here is the Digital Color Postmark for this issue: It measures 2.9″ x 1.4″. The B&W postmark is the standard 4-bar FDOI.

Updated June 23rd: The first day ceremony for this issue will be held Tuesday, August 2, 2016 1:00 p.m. at the Mandalay Bay Convention Center (South Seas Ballroom F, 3950 S Las Vegas Blvd., Las Vegas). The dedicating official will be Chief Marketing and Sales Officer and EVP James Cochrane (right).

Updated May 23rd: These stamps will be issued Tuesday, August 2nd, in Las Vegas. From the USPS:

SuperZoo, National Show for Pet Retailers
The Mandalay Bay Resort
South Seas Ballroom #F
3950 S Las Vegas Blvd
Las Vegas, NV 89119

BACKGROUND: The 20 Forever stamps feature photographs of some favorite pets: dog, puppy, cat, kitten, betta fish, goldfish, iguana, snake, gecko, hermit crab, tortoise, hamster, guinea pig, gerbil, mouse, chinchilla, rabbit, parrot, parakeets and a horse.”

Note that the address above is for the first-day ceremony, not the FDC servicing address.

Added April 27th: Still no word when these stamps will be issued. I checked.

Added November 4th: I brought your qualms about the legality of each and every one of these pets in all states to the attention of Mary-Anne Penner, chief of USPS Stamp Services. She replied that, upon investigation, the legality of owning a particular pet can be very complex, and is also governed by state, county and even local laws and neighborhood rules, “and can change quickly.”

However, she stands by the identification of the bird: “The bird in the stamp art is a canary winged parakeet. The birds are also called white winged parakeets (Brotogeris versicolurus). We confirmed this with the photographer and a veterinarian who specializes in birds.”

From the USPS August 20, 2015:

20 designs
FDOI: Second Quarter (National Pet Month is in May)
Format: Booklet of 20

This issuance celebrates America’s love of pets.

The stamp art for the Pets booklet features 20 existing photographs. Each photograph represents an animal we love from these groups: puppies, betta fish, iguanas, hamsters, goldfish, parrots, guinea pigs, tortoises, rabbits, kittens, corn snakes, mice, hermit crabs, chinchillas, gerbils, dogs, parakeets, horses, cats, and geckos.

Existing Photos: Eric Isselée
Art Director: Derry Noyes

Notes: Stamp Services chief Mary-Anne Penner says the USPS made sure that it is legal to own all of these pets in all 50 states. There have been requests for a Ferrets stamp, but ownership is not legal throughout the U.S.